begins class和classes begin为什么加s?

begins class和classes begin为什么加s? Class begins为什么Begin要加S 是Class begin.还是Class begins.还是Classes begin.为什么? 为什么classes begin中classes变class时,begin变begins the next class begins at half past nine.begin 为什么加s classes begin at ...和class begins at ...它们有什么区别? what begins fall from the trees.begin为什么加s our story begins的begin为什么加s? Let's _____our class.begin begins classes begin begin要不要加s? "class begin"还是"classes begin"? what begins to fall from the thees?这个begin为什么加s