A) In the voting for last year’s Worst Business of the Year award, Chapter earned at least three times as many votes as did the second-most hated company.
Not relevant. Does not address the causality (Customer service -> votes for WBA).

B) The quality of a company’s customer service affects some of the voters for the Worst Business of the Year award.
Correct. In line with assumption 2, though some has a little bit of ambiguity attached to it. We can negate to be certain, and get back to this after checking other options.
Negated: the quality of Customer service does not affect any of the people who vote for WBA. This will definitely break the conclusion. Hence, option B is the correct choice.

C) Internet providers are not the only businesses in the running for the Worst Business of the Year award.
Not relevant. Does not address the causality (Customer service -> votes for WBA).

D) If Chapter did not hold a monopoly in the high-speed internet industry, market forces would compel it to provide better customer service.
Does talk about Customer Service but does not address the effect of the causality. This does not tell us anything about how Customer Service impacts votes for WBA. Hence, no impact on the conclusion.

E) Voters for the Worst Business of the Year award are not influenced by previous years’ results.
Tricky choice. The issue is that even if voters are influenced by last year's results, if last year's results are because of the poor customer service, then the root cause would still be customer service.
Poor Customer Service = A. Votes for WBA = B. Last year's results = C.