firms that use

Question

Firms that use computers have found that the number of the staff _________is needed for quality control can be substantially reduced.
A whose B as C what D that
答案是哪一个 为什么?

Answer 1

D
使用计算机的那些公司早就发现质量控制所需要的工作人员数量可以大幅度减少.
这句话主要结构：
Firms..have found that the number of the staff.can be...reduced.
that use computers 定语从句修饰firms, 使用计算机的公司
that is needed for quality control 定语从句修饰the number of the staff,质量控制所需要的人员数量
在此,that指代the number of the staff
what不能引导定语从句,先排除C.
因为that在从句中作主语,再排除A.
as单独不能引导限制性的定语从句,也排除.
所以选D.