Sometimes when their trainer gives the hand signal for Do

It is scary to differ.

I will go with (B)

Anandnk, even though dolphins give different responses to the same hand signal, what proves that there was no stimuli in doing so? What we really want to prove is that there was no stimuli behind all of that as said by the next to last sentence.

I just thought that since the response is different each time the dolphins are just thinking for themselves.
I may be dead wrong by splitting hairs.

Paul, how can we assume that natural habitat lacks stimulus.

Karthik,
I am sure Paul will add his comments. My take (the reason why I choose) is that

If Dolphins can intelligently respond different actions for the same types of communication (for same hand signal or whistles), means they have residual intelligence - much beyond what has been witnessed in captivity. This would be the paraphrase. E establishes the paraphrase.

B restates (the fact that they respond to the same signals differently) what's already provided as evidence. So, B is out.

A stimuli, in the context of the argument, is a human induced one:
when their trainer gives the hand signal
In their natural habitat, dolphins would of course be living without the presence of any such stimuli

I'm also going on a limb here and stating B.

Conclusion:

"Dolphins are capable of higher cognitive functions that may include the use of language and forethought."

Support for this argument:

"Hand signal indicates do something in tandem" (in the stimulus)
+ "Doing something new tandem (not learned) via hand signal" (B)
+ "tandem action demonstrates higher cognitive function" (assumption)

= Conclusion

I think E is irrelevant, because they do these behaviors in the environment in absence of a hand stimulus doesn't imply "forethought, or language", it may just show an intuitive behavior. B states they they can activily create new manuevers.

What is the Official Answer?

https://www.tol24.com/market/mba/images/gmat_lsat.doc

Found that link on google, according to that, it states the answer is B.

B is the answer. I will write the explanation later

Got it B as FA.

You show the hand to delphins and they do something together, the first response is say learned, but the second response is not since if they learned to go round they will react in the same manner even next time, since they do not respond in the same way, it implies that they have some level of cognitive functions which make them interact with each other and respond in tandem.

A lite one:

dolphin1: the trainer says go round and then jump
dolphin2: lets do it
dolphin1: he moved his hand again,
dolphin2: lets not do that again (contrary to what that Shrek donkey says)

Well, although B is the answer I can challenge it. What if dolphins, with the trainer's hand gestures, are doing those new "complex" moves because they have no recollection of the exact move they are supposed to do. Thus, can we call them intelligent?

If they are coordinated with one another, yes

You got a point