If she _______________ how to calibrate the instrument, she _______________ done the experiment.
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Answer: C
This sentence is a classic example of a third conditional sentence, which is used to describe a hypothetical situation in the past and its imaginary past outcome.
The standard grammatical structure for the third conditional is:
If + Past Perfect, ... would / could / might + have + Past Participle
Applying this structure to the given sentence:
- If-clause: "If she had known (past perfect) how to calibrate the instrument..."
- Main clause: "...she could have (modal perfect) done (past participle) the experiment."
Let's evaluate the options:
- Option A (knows, will have): Incorrect tense combination (mixes present simple with future perfect).
- Option B (knew, had): Incorrect structure for a past hypothetical condition.
- Option C (had known, could have): Correctly follows the third conditional structure.
- Option D (should have known, would have): Grammatically incorrect in the conditional clause.
Therefore, the correct option is C.
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