下列家庭小实验不能成功的是（　　）

A．用食盐水除水垢

B．用加热的方法给聚乙烯塑料袋封口

C．用铅笔芯代替石墨试验导电性

D．利用洗洁精的乳化作用清洗餐具上的油污

在下列各句的空白处填入一个最恰当的单词，使句子意思完整，语法正确。

1.  The two boys look very_______. Maybe they are twins.

2.  When my bike doesn't work, my father can______it.

3.  We will think up some_______to solve the problem.

4.  Could you please hand these books_______? We'll use them in class.

5.  I think Uncle Zhang can help_______up the watch.