Sentence Correction

With answer choice E, the sentence goes like:

El Nino, the periodic abnormal warming of the sea surface off Peru, is a phenomenon where ocean and atmosphere changes are combining and allow the warm water accumulating in the western Pacific to flow back to the east.

Although I understand why this option is incorrect, I am wondering whether "are combining" and "allow" correctly parallel with each other, regardless what the sentence intends to convey. I just want to reinforce my understanding on some basic yet important parallelism rules.

BTW, the correct sentence is:

El Nino, the periodic abnormal warming of the sea surface off Peru, is a phenomenon in which changes in ocean and atmosphere combine to allow the warm water that has accumulated in the western Pacific to flow back to the east.

Would someone please help? Thanks![/u]

"are combining" and "allow" are not parallel to each other. make sure that both the side of the sentecnes are both structurally and logically parallel.
eg: the division was opening offices, hiring staff and investing in equipment. (opening, hiring and investing are parallel
eg: Sal applied himself in his new job, arriving early every day, skipping lunch regularly, and leaving late every night (applied is the main verb where as arriving, skipping and leaving provide additional information about how Sal applied himslef).
Hope this helps

Primarily, where is not the correct word to refer a phenomenon.

Secondly, placing and would mean that the environmental changes are combining. the environmental changes allow XYZ. These are not two different elements which result from environmental change.
the sentence means "the environmental changes combine in order to allow XYZ."