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Difficulty: HardModal Auxiliaries and Expressing Modality

Complete the sentence below by supplying the correct modal verb phrase that expresses an unfulfilled past obligation.

Answer:The safety inspector noted that the plant engineer 【should have】 calibrated the pressure relief valves prior to initiating the turbine sequence, as mandated by the operational guidelines.

Answer

The correct modal phrase to complete the blank is 'should have' (or 'ought to have').
The sentence context establishes a past requirement that was mandated by official guidelines but not performed prior to initiating the turbine sequence. In English, an unfulfilled obligation or duty in the past is expressed using the perfect modal auxiliary structure 'should have' or 'ought to have' followed by the past participle of the main verb.

Step-by-Step Solution

1
Analyze the temporal context and situational meaning of the sentence.
The sentence refers to a past procedural requirement ('prior to initiating', 'mandated by guidelines') that was neglected or not carried out.
Identifying that an action was necessary in the past but remained unfulfilled dictates the choice of past modal structure.
2
Identify the modal construction required for past unfulfilled obligation.
The perfect modal construction consisting of 'should' or 'ought to' + 'have' + past participle ('calibrated') is required.
Simple modal auxiliaries express present or general modality, whereas perfect modals (modal + have + past participle) convey past obligation or advisability that was not realized.
3
Verify acceptable grammatical variants.
Both 'should have' and 'ought to have' correctly complete the sentence with identical semantic force.
'Ought to' and 'should' are synonymous modal expressions of duty, obligation, and correctness.

Key Concept

Unfulfilled Past Obligation via Perfect Modal Auxiliaries
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Topics

Modal Auxiliaries and Expressing Modality

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