下列是美国前总统尼克松的两段讲话，对此理解有误的是（  ）

—Sorry, Mr. Smith isn't        now. Can he call you back later?

请在如图所示家庭电路中，以笔画线代替导线，将一个两孔插座和一个带按钮开关的螺口灯泡接入电路.

根据对话的情景，从方框中选择适当的句子填在画线处，使对话完整通顺。其中有两项是多余的。
A: Hi, Zhou Yanhong. ____ 
B: I'm reading a book.
A: Oh, do you like reading?
B: Yes, very much. _____ 
A: I like playing the piano.
B: Good. By the way,____ 
A: It's easy and interesting. I like it a lot.
B: But I think it's difficult and boring. ____ I like Chinese best.
A: ____ 
B:Because I think it's useful (有用的) and interesting.