GATE CS 2014 Set 3 Q.2 (GA Q.2): Verbal Ability and Grammar

If she _____ how to calibrate the instrument, she _____ done the experiment.

knows, will have

knew, had

had known, could have

should have known, would have

Official answer and solution

Solution

Apply the standard grammatical structure for a third conditional sentence expressing a hypothetical past event.

The sentence refers to an unfulfilled hypothetical situation in the past, indicated by the past participle "done":
"If she [] how to calibrate the instrument, she [] done the experiment."
In a third conditional sentence:
- The "if"-clause takes the past perfect tense: had + past participle (had known).
- The main result clause takes a modal verb with have + past participle: could have / would have + past participle (could have done).
Substituting the options:
"If she had known how to calibrate the instrument, she could have done the experiment."

This correctly matches option C.

Final answer

Common trap

Selecting option B ('knew, had'), which produces 'she had done' instead of the required modal auxiliary 'could have done'.

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

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