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Question

Difficulty: MediumModal Auxiliaries and Expressing Modality

Complete the sentence below by filling in the blank with the appropriate modal verb phrase that expresses strong past logical deduction based on the available evidence.

Answer:Considering that the laboratory security door was locked from the inside and the primary keycard remained on the main desk, the researcher 【must have entered】 through the emergency ventilation shaft.

Answer

must have entered
The sentence presents clear evidence (a door locked from inside and a keycard left on the desk) from which a strong logical conclusion must be drawn. The construction 'must have entered' correctly combines the modal verb of logical deduction 'must' with the perfect aspect 'have entered' to express high certainty about a past action.

Step-by-Step Solution

1
Identify the contextual function of the modal verb needed in the sentence.
The clues ('locked from the inside', 'keycard remained on the main desk') present logical proof pointing to a single past conclusion.
When evidence strongly points to a certainty about a past event, English grammar requires a structure of logical deduction.
2
Construct the past logical deduction phrase using the appropriate modal auxiliary.
'must' + 'have' + past participle verb ('entered' / 'accessed').
'Must have' followed by a past participle expresses certainty or logical conclusion regarding an action in the past.

Key Concept

Modal Auxiliaries for Past Logical Deduction
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Topics

Modal Auxiliaries and Expressing Modality

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