Institution: জাতীয় কবি কাজী নজরুল ইসলাম বিশ্ববিদ্যালয় (JKKNIU) Exam: ক ইউনিট || জাতীয় কবি কাজী নজরুল ইসলাম বিশ্ববিদ্যালয় || 2013
Topic: Right Form of Verb, Subject: English Grammar (ইংরেজি গ্রামার)

Best Answer Explained in Below-:

The sentence describes a situation involving two events that occurred at different times. The first event is "I saw John last Sunday," and the second event is "he was tired." To explain why "C) had been to" is the correct choice, we need to understand the concept of past perfect tense.

The phrase "he had been to a party the night before" uses the past perfect tense, which is employed to indicate an action that occurred prior to another action in the past. In this context, John's attendance at the party happened before I saw him last Sunday, making it a fitting choice to clarify the sequence of events.

The other options do not correctly represent the timeline:

A) "was to" implies a scheduled future event,
B) "has been to" suggests a relevance to the present, which is not applicable here,
D) "could be to" implies possibility or capability and does not fit the context.

Thus, "had been to" accurately sets up the causal relationship between John's prior attendance at the party and his tiredness when we met, highlighting the connection between the two past events effectively.