张先生夫妇没有儿女，收养了一位来自地震灾区的孤儿组成家庭。这样组合而成的家庭属于[ ]
A．核心家庭
B．主干家庭
C．联合家庭
答案：A
— When did it begin to snow?
— It started _____ the night.[ ]
A. during
B. by
C. in
D. at
锅炉给水除氧过程中PH值在（）时反应速度最大。
A.9~11
B.10~11
C.9~10
D.10~12
