用所给单词及其正确形式填空。

1. — Where is Jim now?

    — He ____ (water) some flowers in the garden.

2. — What's your plan for the coming holiday?

    — I ____ (visit) Beijing if possible.

3. They _____ (talk) about the TV play when I came into the room yesterday.

4. The medicine must ____ (keep) away from children.

5. I'm a little weak in physics. But my uncle is too busy _____ (help) me.

6. It ____ (be) two months since we met last time.

7. There _____ (be) a class meeting after class this afternoon, isn't there?

8. You don't need ____ (copy) the new words now.

9. Don't move unless you ____ (tell) to.

10. I happened ____ (meet) Mary's friend in the street yesterday.

函数z=f(x，y)在点P(x，y)处的偏导数

为连续函数，是函数z=f(x，y)在点P(x，y)处可微分的( )。

A．充分条件

B．必要条件

C．充分必要条件

D．既非充分也非必要条件