求教prep1-24，比较问题头大阿！

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

现在搞不清楚什么时候用low，什么时候用less。这题如果只有less than, 只保留介词短语比较可以吗？

头大，比较好易混

less指数字多少的比较，low指实际的高度的比较

is A the key answer?

这块也是我的薄弱之处....高手请赐教！

求解

lower和less的区别搞不是很懂，但是they did 应该可以省略，因为比较中，比较从句的主语和谓语一样时，可以全部省略，留下作状语介词

同意楼上的，不过做了不少题好像状语比较都是把主谓补出来的。XDF说数字比较只能用LESS