Sentence Correction (SC) | Re: Employment costs rose 2.8 percent in the 12 months that

I'm curious about this question. Isn't less only used when the quantity cannot be counted? In this case, we are given a concrete number - 2.8. Shouldn't that mean that less cannot be used

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