Critical Reasoning (CR) | Re: Addiction to nicotine in cigarettes prevents many people from quitting

Why is A wrong?

Conclusion: the proportion of Tarnians attempting to quit smoking who succeed in their efforts will probably increase significantly during these five years.

Negating (A) gives: The strength of a person's nicotine addiction DOES NOT depend SOLELY on the amount of nicotine that person regularly consumes.
So, there might be other factors, phychological, for example. The conclusion is talking about Tarnians, who are attempting to quit. So, if there are other factors, the proportion