What does a "fluid" environment suggest about an environment?

A fluid refers to a substance that has no fixed shape, such a substance is capable of flowing and it has little capacity to oppose external stress. In the same sense, a fluid environment refers to an environment that is subjected to continuous changes, the environment is very dynamic and nothing remain stationary for a long period of time. Sometimes the changes can be predicted based on what is currently happening, at other times, the changes may not be predictable before they occur. Thus, a fluid environment refers to an environment that keeps changing all the time.

the answer is a or when it says crossing over

      n