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Question

Difficulty: MediumVerbs, Tenses, and Aspect

Complete the sentence below by supplying the grammatically correct form of the verb in the blank space.

Answer:The safety officer instructed the technicians to inspect the emergency valves daily lest the cooling system 【fail】 during peak operations.

Answer

The correct form to fill the blank is 'fail' or 'should fail'.
The conjunction 'lest' (meaning 'for fear that' or 'to avoid the risk of') requires either the present subjunctive form (the bare infinitive 'fail') or 'should' followed by the bare infinitive ('should fail'). Present indicative, past indicative, or alternative future modals are grammatically invalid in this construction.

Step-by-Step Solution

1
Identify the conjunction introducing the subordinate clause.
The subordinate clause is introduced by the conjunction 'lest', which expresses a precaution against an undesirable event.
The conjunction 'lest' dictates specific rules of mood and modal usage in English grammar.
2
Apply the verb form rule governing clauses introduced by 'lest'.
In formal English grammar, 'lest' requires the present subjunctive mood (the bare infinitive form 'fail') or the modal auxiliary 'should' combined with the bare infinitive ('should fail').
Standard indicative forms (such as 'fails', 'failed', or 'will fail') cannot be used in a clause introduced by 'lest'.

Key Concept

Subjunctive mood after 'lest'
Estimated Time:1m 0s
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Topics

Verbs, Tenses, and Aspect

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