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).