1. 根据语境从方框中选择恰当的单词填空，有的需要变换形式。每词限用一次。

truck,   experiment,   wheel,   chemistry,   sand,   communications

1. （1） The students were doing a(n)in the lab at this time yesterday．
3. （2） Some children are playing withon the beach happily．
5. （3） Tom checked the fourof his car and found nothing wrong．
7. （4） I don't know how it is going because there are noin that area．
9. （5） A(n)stopped behind the house and two people jumped off．
11. （6） Sam is a(n)teacher and he is very friendly to us．