英语 助动词就是帮助行为动词构成否定和疑问的无意义的动词.助动词主要用于句子中的哪些位置

助动词是帮助构成句子的时态,语态以及否定句和疑问句的.常见的助动词有 be ,do ,does ,did ,will .shall ,would ,have ,has ,had 等.
eg 进行时态中的 be doing ,be 就是 助动词 ,be 可以是 am / is / are / was / were
将来时态 中的 will/shall/would do 中 will/shall/would 就是助动词.
完成时态中 have/ has / had done 中,have/ has / had 就是助动词.
在否定句和疑问句 He doesn't study hard .Does he study hard 这两个句子中 Does 帮助构成否定或疑问句,也是助动词.