-Are you sure you can do well in the final exam?  

-_____________, I’ve got everything ready.[ ]

A. No, I’m not sure                                

B. It’s hard to say

C. Yes, I think so                                  

D. I hope not

接头连接泄漏的原因是：接头锥面有划伤；球面活接头表面有划伤；接头体和球接头加工不合格；连接不同心；连接表面有异物或（）不合适等。