有甲、乙两只口袋，甲袋装有4个白球2个黑球，乙袋装有3个白球和4个黑球．

（Ⅰ）若从甲、乙两袋中各任取出2球后并交换放入袋中，求甲袋内恰好有4个白球的概率；

（Ⅱ）若从甲、乙两袋中各任取出1球后并交换放入袋中，求甲袋中白球个数ξ的概率分布和数学期望．

用括号中的介词填空。

(on, like, after, at, in, of, under)

1. Is Li Lei ______ duty today?

2. My bike isn't ______ the tree. It's in the house.

3. What are these ______ English?

4. －Where is the broom?

    －I think it's ______ the floor.

5. －What's on the wall?

    －It's a map ______ China.