“It was a thrilling experience to be whizzed in a “lift” a quarter of a mile heavenward, and to see New York spread out like a marvellous tapestry beneath us. There was the Hudson – more like the flash of a sword-blade than a noble river.” I hope this answer helps you with what you are looking for.
Answer:
A.
Explanation:
To find out if a call of an animal is missing.
It would be A. because the selection said, "The more scientist's listen to these kind of recordings, the more they notice when expected call are missing".