Find out whether there is any grammatical error in below sentence.
The single biggest gainer in this process / was ITC's Gold Flake Kings sales are estimated / to have moved up from 50 million to 200 million sticks per month during 1987 and last year.

A. The single biggest gainer in this process

B. was ITC's Gold Flake Kings sales are estimated

C. to have moved up from 50 million to 200 million sticks per month during 1987 and last year

D. No error

Answer: Option B

Solution(By Examveda Team)

was ITC's Gold Flake Kings sales of which are estimated' or 'whose sales are estimated