Do I have to repeat prepositions within enumerations?

123nobody321 wrote:Hi guys,

I have a quick question regarding the need for a preposition in enumerations. The overall topic is "parallelism".
I made a flashcard that says that we do not need to repeat the preposition (e.g. to, in, by, from etc.) within an enumeration. But I just answered a question which does repeat it.

Here it is:

Hundreds of species of fish generate and discharge electric currents, in bursts or as steady electric fields around their bodies, using their power either to find and attach prey, to defend themselves, or also for communicating and navigating

Answer choices are:
1) either to find and attach prey, to defend themselves, or also for communicating and navigating
2) either for finding and attacking prey, defend themselves, or for communication and navigation
3) to find and attack prey, for defense, or communication and navigation
4) for finding and attacking prey, to defend themselves, or also for communication and navigation
5) to find and attack prey, to defend themselves, or to communicate and navigate

The right answer choice is (5) which repeats the "to" (to find...to defend...to communicate).

Can somebody please explain why it repeats the preposition? Do I always need to repeat it? I am confused now :S

Answers are much appreciated!

Best,
nobody