当保证气密试验的安全性，做气密性试验试验，有必要经（）合格后方能进行。
参考答案：水压试验
用适当的词填空。
1. Mrs Li arrives __________ Beijing at 2: 00 in the afternoon.
2. Thank you __________ your gifts.
3. __________ the girl speak Chinese? Yes, she does.
4. What do you do __________ Sundays?
