形式主语的问题

zqw2001126

It is good form to use the name of the person _______ .

A .who are greeting

B. you are greeting

C. which you are greeting

D. greeting for you

请问为什么答案是B ? 不是很理解形式主语方面的问题

consonant

宾语从句省略引导词that

=the person that/who you are greeting

zqw2001126

有道理,谢谢大虾指点