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Difficulty: MediumModal Auxiliaries and Expressing Modality

Which modal auxiliary verb phrase best completes the sentence to express a logical deduction of past impossibility?

'During the trial, the prosecution demonstrated that the questioned deed contained a watermark first produced in 2018; therefore, the defendant _______ the document in 2015 as claimed.'

  1. could not have signedAnswer
  2. B
    must to not have signed
  3. C
    might not can sign
  4. D
    should not sign

Answer

The phrase 'could not have signed' is the correct choice because it conveys a logical deduction that a past action was impossible given the chronological evidence.
The phrase 'could not have signed' accurately conveys negative logical deduction regarding a past event. Given that the paper's watermark did not exist in 2015, it was logically impossible for the defendant to have executed the deed at that time.

Step-by-Step Solution

1
Analyze the context and timeframe of the sentence.
The event refers to a past claim (2015) refuted by evidence established later (2018).
The modal structure must reflect past time aspect.
2
Identify the intended modality meaning.
The sentence requires a modal of logical deduction expressing past impossibility.
It is logically impossible for a document to exist in 2015 with a watermark created in 2018.
3
Select the correct modal form.
'Could not have + past participle' expresses negative logical deduction in the past.
Modal auxiliaries do not take infinitival 'to' and cannot be combined into double modals.

Key Concept

Modal Auxiliaries for Past Logical Deduction
Estimated Time:50s
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Topics

Modal Auxiliaries and Expressing Modality

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