PREP上的一题目不明白．．．．拜托大家

employment costs rose 2.8percent 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

key:a

这里的ＬＥＳＳ和ＬＯＷＥＲ　的用法有什么不同呢？

lower表程度不符句意