用所给单词的适当形式填空。

1. Giraffes like eating the            (leaf) of trees.

2. Dogs are very            (friend) to us. They can help us a lot.

3. We want to see the koalas            (one).

4. How many            (monkey) can you see?

5. What is it? You can have three            (guess).

按物资在生产中的作用，可分哪几类？