缓冲层铺设时，工程上一般采用射钉和（）相配套的机械固定方法，应用暗钉圈固定塑料防水板，最终形成无钉孔铺设的防水层。
参考答案：塑料垫圈
如图所示，欲使电灯L3发光，在电路中必须将
A．S3闭合，其它可不闭合
B．S2、S3同时闭合
C．S1、S3同时闭合
D．S1、S2、S3都同时闭合
用括号内单词的适当形式填空。
1. The children are very _____ (excite) when they get a lot of presents.
2. There are so many _____ (build) that I can't find the right place.
3. My shoes are _____ (wear) out.
4. Congratulations on crossing the channel _____ (success)!
5. He's _____ (see) the film many times before.
