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Question

Difficulty: MediumVerbs, Tenses, and Aspect

Complete the sentence below by entering the grammatically correct verb phrase in the blank provided.

Answer:If the flight controller 【had detected】 the distorted radio signal earlier, the emergency landing would have been executed without delay.

Answer

had detected (or synonymous past perfect verb phrase: had noticed, had identified, had observed)
The sentence follows a third conditional construction, which describes a past hypothetical situation and its unfulfilled result. The main clause uses 'would have + past participle' ('would have been executed'), which requires the dependent conditional clause to take the past perfect tense ('had' + past participle). Therefore, 'had detected' (or an equivalent past perfect construction such as 'had noticed') is the grammatically correct completion.

Step-by-Step Solution

1
Analyze the main clause of the sentence to identify the conditional pattern.
The main clause contains 'would have been executed', establishing a third conditional (past unfulfilled/hypothetical condition) structure.
The third conditional structure is required when describing an imaginary or unfulfilled event in the past.
2
Select the appropriate tense and aspect required for the conditional clause.
The if-clause requires the past perfect tense ('had' + past participle).
In standard English grammar, a past hypothetical condition in the if-clause mandates the past perfect auxiliary 'had' followed by the past participle of the main verb.

Key Concept

Third Conditional Tense and Aspect (Past Unreal Condition)
Estimated Time:1m 0s
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Topics

Verbs, Tenses, and Aspect

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