用所给单词的适当形式填空。

1. There are several(几个)_____ of students in that big school. (thousand)

2. We have two bikes. But there are six people here, so we still need ______(many).

3. There are twelve _____ (wolf) in the zoo.

4. You must eat lots of vegetables and fruit to stay ________ (health).

5.These snakes come from Europe, they are _______(Europe).