句中有谓语动词的话就要用DO DOES,作为助动词；句中宾语是形容词或名词的话就要is are,作为系动词.当句子主语是第三人称时,助动词(do)就要用三单形式does,系动词(is,are)就要用is.另外,当句中主语是单数的话,系动词也要用is.
如Is he a boy?he是三单,所以用is
Are they boys?they 是复数,所以用are
Does he eat meat?eat是谓语动词,所以要用助动词do,因为he 是三单,所以用does
Do they eat meat?eat是谓语动词,所以用助动词do,因为they 是复数,所以就不用does,仍旧用docan must will have呢？