You see one sentence:
The two estimates were subs________ different.
The visible letters and grammar work together. Before different, the sentence needs an adverb. Substantially completes the word and creates the natural phrase substantially different. Substantial belongs before a noun, as in a substantial difference.
Duolingo’s current standalone task is officially named Fill in the Blanks. Its direction is “Complete the sentence with the correct word.” You read a sentence containing one unfinished word and type the missing letters. The official page gives 20 seconds and advises reading the whole sentence before focusing on the word. The task contributes to Reading, Literacy, and Comprehension subscores; the current test structure lists it six to nine times.
This is distinct from Read and Complete, which presents multiple unfinished words in a passage, and from Interactive Reading: Complete the Sentences, where you select words for several blanks in a passage-based interactive set. Interactive Reading: Complete the Passage is the separate task that asks you to select a missing sentence. Here the standalone unit is one sentence and one unfinished word.
There is no official finite word list to predict. Train reusable decisions instead at the Duolingo English Test vocabulary hub and Exam English hub.
Use four constraints
Read the full sentence, then test:
- Visible letters: every supplied letter must remain in order.
- Grammar: what part of speech and form fits?
- Collocation: what word naturally combines with its neighbors?
- Sentence meaning: which completion makes the whole claim coherent?
Do not generate every dictionary word beginning with the visible fragment. Let the sentence narrow the set.
1. Substantial and substantially
Substantial is an adjective meaning large or important in amount, degree, or extent.
The policy produced a subs_______ improvement.
The article a and noun improvement identify an adjective slot: substantial.
The policy performed subs________ better after revision.
Here better needs an adverb: substantially.
The forms do not mean certain, permanent, or caused by one factor. Local grammar decides the suffix; sentence meaning confirms the choice.
2. Prevalent and prevalence
Prevalent means widespread or commonly occurring.
The practice is increasingly prev_____ among small firms.
After increasingly, complete prevalent.
The prev______ of the practice varies by sector.
After the and before of, the noun prevalence fits.
Neither means predominant, which identifies the main or largest item among alternatives. A practice may be prevalent in several regions without being the most common practice.
3. Provisional and provisionally
Provisional marks a schedule, figure, result, or arrangement as current but not final.
The committee published a prov_______ schedule pending approval.
The noun schedule requires the adjective provisional. The phrase pending approval supports the interim status.
The event was prov_________ scheduled for July.
The participle scheduled is modified by provisionally. Do not complete the fragment as provision simply because those letters are visible; a provision schedule does not fit the intended grammar or collocation.
4. Corroborate and corroboration
Corroborate means support an existing claim or finding with additional evidence.
Independent records corr_______ the initial account.
The plural subject takes the verb corroborate.
The claim still requires independent corr__________.
After requires independent, the noun corroboration fits. The verb takes its object directly: corroborate the account, not corroborate with the account.
Spelling matters: both forms begin corrobor-, with double r and one b.
5. Tentative and tentatively
Tentative describes something not yet confirmed or final.
The researchers reached a tent_____ conclusion.
Complete tentative. The conclusion exists, but its status remains open to revision.
The meeting is tent________ scheduled for Friday.
Complete tentatively, the adverb modifying scheduled.
Do not assume tentative always signals weak evidence. It may describe an unconfirmed date or agreement. The noun partner supplies the relevant sense.
Understanding is only the first step.
Lyra Practice helps you retrieve and use high-value workplace expressions in realistic situations until they feel natural.
Start a practice session →6. Predominant: ranking, not spread
Predominant means main, strongest, or most common within a set.
Cost was the pred________ concern among respondents.
The sentence names a ranking, so predominant fits. If the sentence instead says a concern occurs widely across regions, prevalent may fit. The two words can share a topic without sharing the same decision.
The adverb is predominantly:
The sample was pred___________ urban.
7. Negligible and negligent
Negligible describes an amount, effect, risk, cost, or difference too small to matter for the current decision.
The difference between the readings was negl______.
Complete negligible.
Negligent means careless:
The operator was negl_____ in failing to perform the check.
The unfinished words share an opening, but their noun partners and meanings differ. A difference is not careless; an operator is not “too small to matter.”
Visible letters are hard constraints
Suppose the sentence is:
The additional evidence corr_______ the original finding.
Both corroborates and corroborated could make grammatical sentences in some time frames. The visible letters alone do not decide. Look elsewhere in the sentence for tense and agreement. If the supplied fragment or missing-letter count distinguishes the form, preserve it exactly.
Do not delete or replace printed letters in your mental solution. Complete the given word, not a synonym.
Collocation narrows genuine alternatives
Consider:
The figures remain prov_______ until the audit is complete.
Provisional creates a natural status frame, and the until clause names the confirmation point. Provocative might begin similarly in another item, but it conflicts with both spelling and meaning here.
Useful frames include:
- substantial difference / substantially different;
- prevalent among / prevalence of;
- provisional figures / provisionally scheduled;
- corroborate a finding / independent corroboration;
- tentative conclusion / tentatively arranged;
- predominant factor / predominantly rural;
- negligible effect.
These are practice frames, not predictions of test content.
Worked item
The second survey helped corr_______ the original finding.
- Grammar: after helped, a base verb can follow.
- Visible letters: corr- is preserved.
- Collocation: evidence can corroborate a finding.
- Meaning: the second survey supplies additional support.
Answer: corroborate.
Do not choose correlation. It is a noun and would not fit after helped in this frame.
Controlled practice
1. Adjective or adverb?
The results were subs________ higher than expected.
Answer: substantially.
2. Noun or adjective?
The prev______ of remote work increased.
Answer: prevalence.
3. Status word
The totals are prov_______ until verification is complete.
Answer: provisional.
4. Ranking word
Time was the pred________ constraint.
Answer: predominant, provided the sentence establishes it as the main constraint.
5. Confusable family
The difference was negl______ at this scale.
Answer: negligible, not negligent.
6. Verb frame
The new records corr________ the earlier account.
Answer: corroborate if the sentence is present tense with plural records; inspect all supplied letters and context.
A 20-second routine
Because the official duration is brief, use a compact sequence:
- Read the entire sentence once.
- Name the likely part of speech.
- Complete the visible stem mentally.
- Re-read the finished sentence for grammar and meaning.
- Check every typed letter before continuing.
Do not spend the full time debating subtle synonyms when only one completion fits the printed letters.
Learn suffix signals, not isolated endings
Suffixes become useful when paired with a grammatical frame:
- -al often marks an adjective: provisional result, substantial change;
- -ally can create an adverb: provisionally scheduled, substantially different;
- -ence can mark a noun: the prevalence of;
- -ate can mark a verb here: records corroborate the claim;
- -ation can mark the related noun: independent corroboration.
These are tendencies, not universal formulas. Never attach a suffix mechanically to a stem without checking the established spelling and meaning of the complete word.
Diagnose attractive wrong completions
An incorrect completion is often attractive for one genuine reason. It may fit the topic but not the grammar, fit the grammar but not the printed letters, or form a familiar word while breaking the collocation. Name the failed constraint during review.
For “The difference was negl______,” negligent is a real adjective, but its meaning requires a careless person, act, or organization. For “The prev______ of the condition,” prevalent shares the stem but cannot occupy the noun frame. Precise review turns each error into a reusable decision.
Keep the three DET fill tasks separate
- Fill in the Blanks: one sentence, one unfinished word, 20 seconds.
- Read and Complete: a passage containing unfinished words.
- Interactive Reading: Complete the Sentences: a question inside a multi-step reading set with its own interaction.
Advice that belongs to whole-passage reconstruction may waste time on the standalone item. Here, the complete sentence is your context window.
Final check
Ask whether the completion preserves the given letters, supplies the required word class, forms a natural phrase, and makes the entire sentence coherent. Then inspect suffix and spelling. An advanced-looking word that fails one of those tests is not a good answer.
If you want to practise choosing precise word forms from context, try Lyra Practice.
Sources
- Duolingo English Test: Fill in the Blanks
- Duolingo English Test structure
- Duolingo English Test: How the items are scored
- Duolingo English Test: Read and Complete
- Duolingo English Test: Interactive Reading — Complete the Sentences
Related
- DET Read and Complete Word Families
- DET Interactive Reading Fill in the Blanks Vocabulary
- DET Read and Select Vocabulary
- DET Listen and Type Vocabulary
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