Quote:
Researchers have explored the possibility that dolphins are able to be trained to communicate as humans.
Quote:
A) are able to be trained to communicate as humans
Dolphins are not able, incorrect usageQuote:
B) were able to be trained to communicate as humans
Usage of were able indicates past tense which is incorrect; requirement is present tenseQuote:
C) can be trained to communicate like humans can
Usage of like humans is incorrect as like is used to show examples, we are giving comparison between dolphin’s communication as humansQuote:
D) could be trained to communicate as humans
Dolphin communication compared to humans (invalid comparison)Quote:
E) are capable of being trained to communicate as humans do
Clear crisp meaning, indicates that dolphins have the capability of being trained (capability of what?) to communicate as humans (compared to humans) and preposition do (comparison of dolphin communication and human communication)