I think the answer is A.
Elephants observed in Kenya used different trumpeting noises depending on the purpose of their call: some sounds were intended as a warning call, while others to express emotion and to intimidate predators.
A. to express emotion and to intimidate : I can clearly see a parallelism here. See it this way (while other sounds were intended to express emotions and to intimidate predators)
B. intended to express emotion and intimidating - Intimidating is not parallel to 'express emotion'.
C. expressed emotion or intimidated - It's not the sounds that expressed emotions or intimidated predators.
D. were to express emotion or intimidate - 'or' is changing the intent of the oroginal sentence here.
E. intended the expressing of emotion or intimidating - No need to explain
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