锅炉在开始排污时，首先要（）一次阀，然后再慢慢打开二次阀进行排污，在结束排污时，先把二次阀关闭，随后再（）一次阀。
参考答案：打开；关闭
回答问题。
1. When do you usually get up in the morning?
_________________________________.
2. What's your favourite class at school?
3. What do you usually do on the weekend?
4. What's your favourite season in a year?
5. What do you usually do in that season?
6. When do you go to bed?
最可能的诊断是
A．尖锐湿疣B．结核C．硬下疳D．淋病E．外阴癌
