Asource from which organisms generally take elements is called a/an
a. biotic community.
b. reservoir.
c. exchange pool.
d. food web.

C. Exchange pool.

Explanation:

The exchange pool can be define as the pool which includes the elements which are required to be exchanged between the abiotic and biotic components of the environment. This is the part of every biochemical cycle.

On the basis of the above explanation, an exchange pool is the source from which the organisms generally take elements so as to lead their life cycle. For example, the atmosphere is the exchange pool of gaseous elements such as water vapors, oxygen, carbon dioxide and nitrogen. The organisms take oxygen from the atmosphere for respiration and release out carbon dioxide which becomes the part of the atmosphere.

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.