根据首字母提示补全单词，使对话恢复完整。

1. A: W___________ does the rain come from?

    B: It comes f___________ the clouds.

2. A: Where does the cloud c___________ from?

    B: It comes from the v___________.

3. A: W___________ are you going to do tomorrow?

    B: I'm going to p___________ a flower. 

    A: H___________ do you do that? 

    B: First, put a flower seed in the s___________.

    A: What should you do t___________? 

    B: W___________ it. Put it u___________ the sun every day. Then you c___________ see 

        a flower s___________.

焊缝按结构形式可分为（）.

A、对接焊缝

B、角接焊锋

C、塞焊锋

D、端接