从方框中选择正确的句子补全对话。

A: What’s wrong with you, Helen?

B:    小题1:    I have a cold.

A: Bad luck!   小题2: 

B: Oh, but I’m busy now and I must

finish these exercises in the class.

A:  小题3:   He will ask you to

have a rest at home.

B:    小题4:   I don’t want to ask for leave.

A:   小题5:  You’d better lie down and have a good rest now.

B: OK. I’ll ask for leave at once. Thank you very much.

建筑物的六大组成部分中属于非承重构件的是（）。

A.楼梯

B.门窗

C.屋顶

D.吊顶