人防工程火灾疏散照明和火灾备用照明可采用蓄电池作备用电源，其连续供电时间不应少于（）分钟。
A、20
B、30
C、60
D、90
参考答案：B
用所给词的正确形式填空。
1. This is _____________ (I) book. This hook is _____________ (my).
2. This is a _____________ (child). These are _____________ (child).
3. Is this hat _____________ (your)? No, it isn't _____________ (my).
4. What's she doing? She's _____________ (wash) the _____________ (dish).
5. Mrs. Smith is _____________ (cook) eggs for me.
6. Listen! Li Jing _____________ (sing) in the classroom.
7. Jack _____________ (go) to bed at 10: 00 in the evening.
8. Without _____________ (a) umbrella, I'm wet on a rainy day.
9. Here are many _____________ (dress).
10. I want everyone to sing _____________ (loud).
分离液态的（）可以获得氧气，该过程属于（）变化。
