根据句子意思，用括号中所给单词的适当形式填空。

1. Children should speak to old people _______ (polite).

2. Tree-planting Day is on the _______ (twelve) of March every year.

3. David took a lot of ______ (photo) in Mochou Lake Park last weekend.

4. The time is too short.It’s ______ (possible) for Daniel to finish this work.

5. Stephen spends about half an hour ____ (swim) every Saturday afternoon.