His salary as a driver is much higher than ----- .

问题描述:

His salary as a driver is much higher than ----- .
A.a porter B.is a porter C.as a porter D.that of a porter
请教为何选D

指工资高于一类群体而不是一个搬运工,指一类群体的话,就只有D,A一个搬运工,B明显错误,C如一个搬运工.都不是表示一类群体