瓦斯爆炸的界限并不是固定不变的，（）可使瓦斯爆炸界限扩大。

A.惰性气体的混入

B.可燃气体的混入

C.煤尘的混入

D.瓦斯与空气的混合气体温度高

Many children _____ your age are always ____ a good mood to do the things they’re interested in.

A．at, in

B．of, in

C．at, on

D．of, with