Which revision best fixes the mistake in parallel structure in the sentence?

Explanation:

Parallel structure is important in sentences to ensure clarity and consistency. In the given sentence, the options with "to surf" and "to dive" do not maintain parallel structure. The correct revision is "This wet suit is designed for surfing or diving."

It is important to note that parallel elements in a sentence should be of the same grammatical form. In this case, "surfing" and "diving" are both gerunds (the -ing form of a verb used as a noun), making them parallel in structure.

Remember, when faced with questions regarding parallel structure, it can be helpful to read the sentence out loud to identify any grammatical inconsistencies. In this case, choosing the option with "surfing or diving" ensures that the sentence maintains parallel structure and conveys the intended meaning clearly.