为了提高制冷系统的经济性，发挥较大的效益，工业上单级压缩循环压缩比（）。
A、不超过12
B、不超过6～8
C、不超过4
D、不超过8～10
参考答案：B
用所给动词的正确形式填空
1. -Hurry up! It's time to leave.
-OK, I _____ _____(leave).
2. What are you going _____ _____(do) this Sunday?
3. -What _____ you _____(do) these days?
-I _____ _____(make) a model plane.
4. They _____ _____(go) to meet outside the school gate.
5. -What's your plan for the coming vacation?
-I _____ _____(visit) Beijing if possible(可能的).
