根据短文内容，补全所缺的单词。
We can see different signs in public places．Some____tell us what we should do．This sign is____．There is a picture of an animal in the____．It tells us to look out for animals．Some signs tell us what we should not do．We should not smoke in the forest．It____start a fire．That's why we see a "____" sign in the forest．Some signs tell us where to go．The bus and underground signs tell us where to find the stations．
