Although most smoking-related illnesses are caused by inhaling the tar in tobacco smoke, it is addiction to nicotine that prevents most smokers from quitting. In
an effort to decrease the incidence of smoking-related illnesses, lawmakers in Sandonia plan to reduce the average quantity of nicotine per cigarette by half over the next five years. Unfortunately, smokers who are already addicted to nicotine tend to react to such reductions by smoking correspondingly more cigarettes.
The information above most strongly supports which of the following predictions about the effects of implementing the Sandonian government’s plan?
The average quantity of tar inhaled by Sandonian smokers who are currently addicted to nicotine will probably not decrease during the next five years.
Sandonian smokers who are not already addicted to nicotine will probably also begin to smoke more cigarettes during the next five years than they had previously.
The annual number of Sandonian smokers developing smoking-related illnesses will probably decrease during the next five years.
The proportion of Sandonians attempting to quit smoking who succeed in that attempt will probably decrease during the next five years.
The number of Sandonians who quit smoking during the next five years will probably exceed the number who quit during the last five years.
答案是a，how come? why not b?? | 
