两直角刚杆AC、CB支承如图所示，在铰C处受力P作用，则A、B两处约束力与x轴正向所

（737-800）APU向两个空调组件提供引气（）。

A.只在地面

B.只在空中

C.在地面和空中

D.APU不应该用于向两个空调组件提供引气

根据对话内容，在空白处填写适当的话语（话语可能是一个句子，也可能是一个短语或一个词），使对话完整。

Boy:  Hello, Mrs Tan.  I'd like to be a volunteer.   _ 1     ?

Woman: Sure. What kind of volunteer work?

Boy:  Well, I like working with kids.    

Woman: Do you know _   2   _? We need someone to help teach kids to play basketball.

Boy:  No, I don't really like basketball.  Is there anything else?

Woman: Sure.  There's a job cleaning up the parks.  It's every Sunday.

Boy: That's no good.  I have to      3      my grandmother on Sundays.

Woman:  I see.  Here's another job.  Car you fix up bicycles ?

Boy:     4      . I can't even fix up my own bicycle.

Woman: Ummm.  We need someone to read to people at the hospital.  You can do it any day you like.

Boy:      5     .  When do I start ?

Woman: How about today '

Boy: OK.

运行车长换乘时，应及时用列车无线调度通信设备与机车乘务员核对有关列车运行命令，对表和通报姓名。

β＋衰变的实质是母核中的一个（）转变为中子。