Answer:
In the interrogative form, the sentence becomes:
Did they pay the fees before examination?
Step-by-step explanation:
The original sentence is in the affirmative form. The verb "paid" is in the simple past tense. To transform this sentence into negative, we must use an auxiliary that shows the sentence is in the past: "did". We place the auxiliary before the subject "they":
They paid the fees before examination. --> Did they pay the fees before examination?
Note that the main verb does not remain in the past. It goes back to its base form "pay" since the auxiliary already indicates the past tense.