请教：PREP I-24

24.   (25819-!-item-!-188;#058&002130)

Employment costs rose 2.8 percent in the 12 months that ended in September, slightly less than they did in the year that ended in the previous quarter.

(A) less than they did

(B) less than it did

(C) less than they were

(D) lower than

(E) lower than they were

正确答案：A

用they指代costs?怎么觉得不对啊？？

对的亚，

首先，数字的比较不是高低的实物比较排出D E

然后比较结构，A does B this sep, less than C did D last year

A 复数所以C 也是复数 lastyear 过去式