题目内容：

根据句意，在横线上写出括号内所给单词的适当形式

1.Keeping listening and speaking is the ________________ (nature) way to learn a language.

2.Usually________________ (wolf) catch small animals for their food.

3.The man made a lot of money by ________________(sell) a tiger’s fur.

4.The less fast food you eat, the _______________(health ) you will be.