Tian helped her mother cook the dinner yesterday evening.cook为什么不要加ing

help sb do sth.固定形式!因为help是情态动词吗不是，help 是动词help sb do sth一、关于help sb do sth help sb do sth是大家比较熟悉的结构， 通常也可说成help sb to do sth，其意 为“帮助某人做某事”，两者常可通用——即其中的不定式符号to可以省略，也可以 保留。如： We helped her (to) find her things. 我们 帮她找东西。 I helped him (to) repair his bike. 我帮他