The choice B is irrelevant here because it compares brushes used for 6 months with the ones used for 8 months, but both of them are outside the prescribed usage time. We do not care whether it gets more contaminated after 6 months or not.

MGMAT SC guide says that GMAT prefers the use of relative clauses in such cases.

While I purely agree with Ron's explanation and examples, I am still a litle confused about the application of the specific rule to the case in hand.

can you please explain whether the rule applies for comparisions as well?

eg: I ran better than he. (or) I ran better than he did/ran.

I have an issue in understanding parallelism in a particular sentence from MGMAT SC guide. Kindly help me understand that. 'The music company was afraid that the accelerating decline of sales would not be compensated by increased revenue. ' I felt that the 2 modified nouns are not parallel here. I f...