Birds known as honeyguides exhibit a unique pattern of behavior: the bird leads another animal, such as a honey-badger or a human, to a bees' nest with their chattering when they fly ahead; after the larger animal takes honey, the bird eats the wax and bee larvae.

A. with their chattering when they fly
B. with chattering and its flying
C. by chattering as it flies
D. by chattering and its flying
E. by chattering as they are flying

OA is C

I have got the answer, but can anyone please explain how can i eliminate B and D.

Thanks & Regards
Sachin