请你根据句意及所给汉语提示，写出单词的正确形式。

1. My ________ (爷爷奶奶) love me very much.

2. ________ (那些) aren't oranges. They are apples.

3. Linda, is that your________(椅子)？

4. Math is very ________ (有趣) , but it's very difficult.

5. He has________(二十个) ping - pong bails.