Error spotting (run-on & apposition): Identify the erroneous part (A/B/C) — mark D if correct — '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. / No error.' Resolve clause fusion and punctuation.

Issue
Part B improperly fuses two clauses: a copular predicate ('was ITC's Gold Flake Kings') and a new finite clause ('sales are estimated …'). This creates a run-on. It needs separation or proper subordination.

Corrections
Option 1: 'The single biggest gainer in this process was ITC's Gold Flake Kings; sales are estimated to have moved up …'Option 2: '…was ITC's Gold Flake Kings, whose sales are estimated to have moved up …'

Other polish
Time phrase 'during 1987 and last year' is awkward; prefer 'between 1987 and last year' or provide precise range.

Final Answer
B — Clause fusion/run-on: split or subordinate 'sales are estimated …'