There are not any classrooms behind the gym
Is there a big tree in front of the house?
Our school is next to a history museum.
There are 30 students in our class.
There is a dining hall ,a gym and a library in our school.
注:there be(is/are) 句型要注意就近原则,最近的一个名词是单数或不可数名词,就用is;复数名词就用are.