对话填句子 （每空一句）。

A: Do you know Nancy found $100 in the street this morning?

B: Really? What did he do then?

A: 1.                                            . The police wrote down his name and address and told him if no

    one came to get the money in a week, he could get the money.

B: Wow! How lucky he is! 2.                                                ?

A: First, I'd try to look for the owner. Then, 3.                                                . I think the teacher

    could help find the owner. What about you?

B: 4.                                             . My bike has just broken.

在探究实验中要得到可信的结论，一组对照实验中变量只能是（　　）

A．多个

B．1个

C．2个

D．10个