实行重要岗位定期轮换和强制休假制度，对重要岗位人员原则上（）至少轮换一次。
A、一年
B、两年
C、半年
D、三年
参考答案：B
等体积的盐酸和氢氧化钠溶液分别与两份足量铝粉反应，在相同条件下产生相同体积的氢气。则盐酸和氢氧化钠溶液物质的量浓度之比为
A．1：1
B．2：1
C．3：1
D．2：3
动词填空。
1. My uncle with my grandparents ________ (live) in Beijing.
2. Is it time for us ________ (begin) our class?
3. We have fun ________ (swim) in the pool every summer.
4. Mary is clever and can ________ (speak) four languages.
5. I spend about half an hour ________ (chat) with my friends on the Internet.
6. ---Tom, __________(wash) the dishes after supper.
---OK, Mum.
7. Your new friend __________ (sound) good. I want to make friends with him.
8. This pair of shoes________(not be) for Millie. They are for Sandy.
9. Everyone in Mr Wu's class ________ (not do) homework at school.
10. ________ his Chinese and English teachers ________ (come) from the same city?
ss?
r.