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. No error
• B. The single biggest gainer in this process
• C. to have moved up from 50 million to 200 million sticks per month during 1987 and last year
• D. was ITC's Gold Flake Kings sales are estimated

Answer: (D)