是Class begin.还是Class begins.还是Classes begin.为什么?

是Class begin.还是Class begins.还是Classes begin.为什么? "class begin"还是"classes begin"? 是用Class begin 还是Class begins 是class is begin还是class begin begins class和classes begin为什么加s? 为什么classes begin中classes变class时,begin变begins 是class starts 还是class begin 是before class begin 还是before class is begin Class begins为什么Begin要加S Let's _____our class.begin begins classes begin at ...和class begins at ...它们有什么区别? the next class begins at half past nine.begin 为什么加s