When Mary discovered how treacherous the streets could be, she demanded that herboys stay close to her in the church gym and youth center, and the boys were as good as gold, listening to every word she says.

A．very naughty

B．very obedient

C．faithful

D．patient

蒸馏操作是利用各组分（）差异或各组分蒸汽压的差异使它们得到分离。

A.溶解度

B.沸点

C.熔点

D.浓度