classes usually begins at eight o'clock.

classes usually begin at eight o'clock
or
class usually begins at eight o'clock

Classes已经是复数了 Begin就不能加s了吧

^我的想法

有错

Class usually begins at eight o'clock.

Classes usually begin at eight o'clock.

我认为用单数比较好

Classes usually begin at eight o'clock.
That's it.