_____ comes first will be served first.A.Who B.Anybody C.All that D.Whoever理由

_____ comes first will be served first.A.Who B.Anybody C.All that D.Whoever理由
_____ comes first will be served first.A.Who B.Anybody C.All that D.Whoever
理由

_____ comes first will be served first.A.Who B.Anybody C.All that D.Whoever理由
D
谁先到就为谁服务./先到的先享受服务.
whoever comes first 是这个句子的主语,因为它是一个从句,所以叫主语从句.
如果选A,应当在who前面加上Anyone；如果选B,则应当加who；C错在all,因为这里强调的是单数,而all表示复数.

A who
……的人
先来的人先被服务
引导主语从句
先来的优先服务。