"Geared to" is correct in some contexts, but so is "geared toward," and "geared toward" is appropriate when you mean that something is done with a specific purpose. Also, it looks like C either has a parallelism problem or subtly changes the sentence's meaning, depending on how you read it. You either have a list of two items, "enhance athletes' performance" and "their preparation," which would be a verb and a noun, and therefore not parallel, or else "to enhance" applies to both "athletes' performance" and "their preparation," which would mean that the athletes' preparation is being enhanced. It seems that the intended meaning is that the programs are geared toward two things: enhancement and preparation. The correct answer makes that clear in parallel form, using gerunds.

I think C has no problem of parallelism though it changes the meaning slightly.

c) are geared to enhance athletes' performance and their preparation ( "athletes' performance" and "their preparation" are nouns and parallel to one another, and both are enhanced simultaneously )

I will go with [spoiler]'E'[/spoiler]. Please post the OA and quote the source.

Cheers