You are not in good health, I think. You could improve your       by running every day.

A．position

B．situation

C．energy

D．condition

空气中含量最多，化学性质又不活泼的气体是 [ ]

A. 氧气　　

B. 氮气　　

C. 水蒸气　

D. 二氧化碳