Select the correct modal construction expressing past logical deduction:
'The laboratory door was locked from the inside; the researcher ______ through the fire exit.'
Answer and explanation
Correct answer: A. must have left
- Step 1: To express a strong logical certainty about an event in the past based on evidence, English uses 'must + have + past participle'.
- Step 2: The locked door provides evidence leading to the deduction 'must have left'.
Answer
must have left.
Why not the others: 'must leave' refers to present or future obligation; 'can have left' is not used for positive logical deduction in standard English ('could have' or 'must have'); 'ought to leave' refers to present moral obligation.
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