When a number of people ______ together in a conversational knot, each individual expresses his position in the group where he stands.

A．has become an essential part of people's life
B．may well affect the health of the trainees
C．will attract more people in the days to come
D．contributes to health improvement as well

A．how well they could do in athletics
B．what their health condition was like
C．what kind of fitness center was suitable for them
D．whether they were fit for aerobic exercise