Or: the answer that’s correct, exact, and still wrong
Show a C1 class a sentence completion gap with the instruction ‘NO MORE THAN TWO WORDS’ and most will treat it as a soft guideline, close enough is close enough. It isn’t. This is graded with the same mechanical strictness as a spelling test: the wrong number of words, the wrong word borrowed from a paraphrase instead of lifted exactly, or the right words in the wrong grammatical form all fail identically, regardless of how clearly the student understood the passage.
Three conditions, not one. A correct answer has to satisfy all three at once. It has to respect the word count exactly. It has to use the passage’s own wording, not a synonym, however accurate. And it has to fit the sentence grammatically, the right word class, the right number, the right tense if a verb form is required. Most wrong answers satisfy two of the three and fail on the third, which is precisely why they feel correct to the student who wrote them.
A concrete case makes this clearer than any rule statement. A passage says participants who slept under six hours showed ‘a marked decline in short-term memory.’ The gap: ‘linked to a decline in ______ (NO MORE THAN TWO WORDS).’ ‘Memory’ alone is exact and within the limit, but drops information the question is actually asking for. ‘Declining memory’ is close in meaning but fails on two counts at once: it isn’t the exact phrase, and it inverts the sentence’s own grammar. Only ‘short-term memory’ clears all three conditions.
Why this is worth teaching as a discipline, not a tip. The instinct to paraphrase is, everywhere else in language learning, exactly the right instinct, it’s usually the mark of genuine comprehension rather than rote copying. Sentence completion is one of the few places in English study where that instinct actively costs marks. Students need to consciously override a habit that has served them well in every other context, which is precisely why it needs deliberate practice rather than a single mention in passing.
The failure mode worth knowing about. Once burned by writing too many words, some students overcorrect toward answers that are too short, dropping a necessary second word to stay safely under the limit. ‘Memory’ instead of ‘short-term memory’ is this exact error. The word limit is a ceiling, not a target, and the fix is always the same: check the answer against the sentence’s own grammar, not just its length.
I’ve put together a free lesson plan on this exact topic, a worked example breaking down all three conditions, controlled practice, freer question-writing practice, an exam-style task, and a full answer key. Download the Sentence Completion and the Word Limit lesson plan (PDF).