Choose the most suitable option to replace the underlined part of the sentence. If the sentence is already correct, select 'No substitution required'.
Had the research data been verified earlier, the project could complete within the deadline.
Show answer & explanation
Correct answer: A
Explanation
Correct Answer
could have been completed
Explanation
Condition Type (Third Conditional): The sentence uses an inverted conditional structure ('Had the research data been verified...'), which is equivalent to a Third Conditional statement (If the research data had been verified...). This structure describes a hypothetical situation in the past that did not happen.
Grammar Rule for the Main Clause: The standard grammatical formula for the main clause in a third conditional sentence is:
Subject + would/could/might + have + past participle (V3)
Active vs. Passive Voice: Because 'the project' is an inanimate object that cannot complete itself, the main clause must be written in the passive voice. The passive formula for a past modal is:
could + have + been + past participle (V3)
Applying this rule yields the correct phrase: could have been completed.
Incorrect Alternatives:
had completed violates the structural requirement of the conditional main clause and incorrectly uses the active voice.
could completed incorrectly drops the auxiliary helping verbs entirely.
could had been complete is grammatically invalid because the modal verb could must always be followed by the base form have, never had.
Key Points
Word: could have been completed
Meaning: The necessary past-modal passive verb phrase that establishes a grammatically sound hypothetical conclusion.
Grammatical Role: Passive perfect conditional verb phrase (functions as the main predicate matching the past perfect conditional clause).