What are “they" listening for? A. To tell how species of animals are different

B. To hear the heartbeats of many
animals

C. To find out if the call of an animal
is missing

C. To find out if the call of an animal  is missing

Explanation:

The more scientists listen to these kinds of recordings, the more they notice when an expected call is missing.

I hope this helps you in any shape or form.

normally working animals are domesticated and ruled by a master, a domesticator (tamer), to perform basic and important functions on a farm, for example. the value used in this context is animal labor in exchange for food. it is not so much a contrast to the story told by napoleon and the pigs, since the animals of that particular farm also performed functions on the farm through domestication. the only thing is that in this case, who rules them is a pig, also an animal, but very respected, to whom the other animals lent him submission. that's about a strong relationship of dependency between animal and owner.