我国列入职业病名单中的职业癌有（）种。
A.6种
B.8种
C.9种
D.7种
参考答案：B
---Great changes in the past ten years in China.
---I agree with you.
A．took place
B．have taken place
C．were taking place
D．had taken place
离心泵的原理是什么？
