gmat_perfect wrote: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 attack prey, to defend themselves, or also for communicating and navigating.

(A) either to find and attack prey, to defend themselves, or also for communicating and navigating - Incorrect - not parallel. either to not ||el to or also
(B) either for finding and attacking prey, defend themselves, or for communication and navigation - Incorrect - Communication and navigation are nouns, which are not ||el to verbs, finding and attacking. Also 'defend themselves' does not mdify anything.
(C) to find and attack prey, for defense, or communication and navigation - Incorrect - not ||el. Communication and navigation are nouns and not ||el with verbs find and attack. to...for... are not ||el
(D) for finding and attacking prey, to defend themselves, or also for communication and navigation - Incorrect - for...to...also are not ||el
(E) to find and attack prey, to defend themselves, or to communicate and navigate - Correct - ||el

OA: E

gmat_perfect wrote: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 attack prey, to defend themselves, or also for communicating and navigating.

(A) either to find and attack prey, to defend themselves, or also for communicating and navigating
(B) either for finding and attacking prey, defend themselves, or for communication and navigation
(C) to find and attack prey, for defense, or communication and navigation
(D) for finding and attacking prey, to defend themselves, or also for communication and navigation
(E) to find and attack prey, to defend themselves, or to communicate and navigate

OA: E

gmat_perfect wrote:Would any one help?

The idiom is "either XX, or YY"

In the option E, where is the "either"?

(E) to find and attack prey, to defend themselves, or to communicate and navigate.

=> "Either X, Y, or Z" is the idiom, but where is the "either"?

Thanks.