There are twenty classes at our school.一本练习上是at 可为什么是at

There are twenty classes at our school.一本练习上是at 可为什么是at Bob and his classes are not have classes at school中文意思是 There are at -------( little ) 2000 students in our school There are at ____ five hundred students in our school At school there are strict rules————.为什么是to be kept There are at least 30 classes in that school.(改为同义句） there are at least 30 classes in that school改为同义句 We have at( )(little)eighty classes in our school. 首字母填空there are at l__ twenty boys in our class there is a playground at our school为什么用at 不用in Are our teacher at school?改错 Our children are all at school