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Difficulty: HardModal Auxiliaries and Expressing Modality

Despite the sudden power surge that destroyed most electrical appliances in the facility, the sensitive laboratory meters remained completely undamaged, implying that the safety relays _______ automatically before the voltage peaked. Which of the following modal verb forms best completes the sentence?

  1. must have trippedAnswer
  2. B
    might can have tripped
  3. C
    ought to tripped
  4. D
    should to have tripped

Answer

The phrase 'must have tripped' is correct because the structure 'must + have + past participle' expresses a logical deduction or strong certainty regarding a past event based on present evidence.
The structure 'must have' combined with the past participle 'tripped' correctly expresses a logical deduction about a past event based on available evidence.

Step-by-Step Solution

1
Analyze the context and time reference of the sentence.
The event (the surge and preservation of meters) occurred in the past.
Past tense verbs 'destroyed' and 'remained' establish a historical context.
2
Determine the required modality meaning.
The speaker is making a logical deduction (drawing a conclusion of high certainty) to explain why the meters survived.
The introductory word 'implying' signals that a deduction is being made from empirical evidence.
3
Select the correct past modal structure.
'Must have + past participle' ('must have tripped') is the standard grammatical construction for past logical deduction.
Pure modal auxiliaries take bare infinitives, and past deductions require perfect aspect ('have' + past participle).

Key Concept

Modal auxiliaries for logical deduction in the past
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Topics

Modal Auxiliaries and Expressing Modality

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