What results when animals live together in extremely large groups?

a. they rapidly use up resources.
b. they can’t develop their own territory.
c. it becomes easy to divide food.
d. it’s easy to assign hunting responsibilities.

I would say the correct answer is A. they rapidly use up resources.
When there are a lot of animals in one place, they tend to fight for food rather than share like humans. This is why their resources won't last for a long time because there are just so many of them in the same group. 

The answer would be sand and gravel

To kill bacteria from our body especially from stomach