There_____three classes in the afternoon.

There_____three classes in the afternoon.
There_____three classes in the afternoon.

There_____three classes in the afternoon.
填are,因为three是三的意思,所以一定是复数,复数的be动词是are.如果不明白还可以追问哦

There_are____three classes in the afternoon.

are

are 不过三节课的确是有点多

are

There are three classes in the afternoon.