Critical Reasoning (CR) | Re: A system-wide county school anti-smoki

A system-wide county school anti-smoking education program was instituted last year. The program was clearly a success. Last year, the incidence of students smoking on school premises decreased by over 70percent.

Which of the following, if true, would most seriously weaken the argument in the passage?

(B) Most students who smoke stopped smoking on school premises last year continued to smoke when away from school.
(C) Last year, another policy change made it much easier for students to leave