Most of the time being can be eliminated since it is usually redundant. However, there are some questions on the gmat where being is acceptable if the other answer choices contain an error.

A)Incorrect - As is used to compare actions so we need to end with as humans do
B)Incorrect - Were is the incorrect tense and the word like is used to compare nouns. Here we are focusing on comparing how dolphins and humans communicate not dolphins and humans.
C)Incorrect - The use of like is used to compare nouns not actions. Here we are comparing the ways dolphins can communicate and the ways humans can.
D)Incorrect - Could is the incorrect tense. As is used to compare actions so we need to end with as humans do
E)Best Answer - being indicates process and is used correctly here although the sentence could be written better.

IMO: E

hwiya320 wrote:Researchers have explored the possibility that dolphins are able to be trained to communicate as humans .

are able to be trained to communicate as humans
were able to be trained to communicate like humans
can be trained to communicate like humans can
could be trained to communicate as humans
are capable of being trained to communicate as humans do

Correct answer : E

I thought Sahil's note mentions how "being" is usually incorrect in the SC?

"Being" is needed because it means "to be trained" but "to be trained" stands after "of", so "to be trained" becomes "being trained"