Topic: Sequence of Tense,

Best Answer Explained in Below-:

The phrase "It is high time we --- home" calls for a specific grammatical structure that conveys urgency about an action that should have happened earlier. The phrase "high time" is commonly followed by the subjunctive form of a verb, which reflects a suggested or recommended action rather than a factual statement.

Among the options given, "C) returned" fits perfectly. The construction "It is high time we returned home" suggests that the speaker feels it is overdue for them to go home, emphasizing the necessity of the action. The verb "return" employs the simple past form in this context, aligning it with the subjunctive mood.

On the other hand, "A) return" would imply a present-tense or habitual action, while "B) had returned" and "D) had been returned" suggest a completed action in the past, neither of which conveys the urgency implied by "high time." Therefore, "C) returned" is the correct choice, as it effectively communicates the idea that the speaker believes it is overdue for them to go home.