At five she was _____ by her mother, who was a famous dancer when young, to go into training. 

A．led

B．enjoyed

C．imagined

D．forced

不属于影响爆炸极限的因素有（）

A.可燃气体的浓度

B.可燃气系的初始温度

C.火源能量

D.体系中惰性气体含量