4. Drivers have to obey traffic rules. If not, accidents may occur.
The correct answer is A. Unless drivers obey traffic rules, accidents might occur.
Explanation: "Unless" means "if not". Option A correctly uses this to express the same conditional meaning as the original sentence. "Might" is a suitable modal verb indicating possibility, similar to "may".
5. The soccer match wasn't cancelled because it didn't rain.
The correct answer is A. If it rained, the soccer match would be cancelled.
Explanation: The original sentence states that the lack of rain was the reason the match wasn't cancelled. Therefore, the opposite scenario would be that if it had rained, the match would have been cancelled. Option A correctly expresses this counterfactual conditional in the present/future.

a
b