Select the most appropriate word to fill in the blank:
My father was very distant, but I suppose all men of his generation _________.

The correct answer is (d) were.
Explanation:
Since the sentence refers to men of his generation (plural subject), the correct verb form is "were."
Meanings of all options:
· There: A place or position.
· Was: Past tense of "be" for singular subjects.
· Would: Expressing a habitual action in the past.
· Were: Past tense of "be" for plural subjects.
Correct sentence:
"My father was very distant, but I suppose all men of his generation were."