Exercise cart affect our outlook on life, and it can also help us get rid of tension, anxiety and frustration. So we should take exercise ______.

A．When he is in a new environment, he is always frightened.
B．When he plays football, he cannot learn new tricks.
C．When he sees a friend, it' s hard for him to remember his name.
D．When he finds a hammer, he cannot tell anything about it.

A．researchers
B．members
C．employees
D．personnel