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．