Understanding the argument -
Since smoking-related illnesses are a serious health problem in Normark, and since addiction to nicotine prevents many people from quitting smoking, the government of Normark plans to reduce the maximum allowable quantity of nicotine per cigarette by half over the next five years. - There is a plan and two causes for the plan. The goal is to reduce smoking-related illnesses.
However, reducing the quantity of nicotine per cigarette will probably cause people addicted to nicotine to smoke more cigarettes. - contrast with "however," and the plan seems to have the opposite of the intended effect.
Therefore implementing this plan is unlikely to reduce the incidence of smoking related illnesses. - Conclusion
We have to strengthen the conclusion. What conclusion? "This plan is unlikely to reduce the incidence of smoking-related illnesses."
Option Elimination -
(A) Over half of the nonsmoking adults in Normark have smoked cigarettes in the past. - how does it even relate to the scope of the argument, which is to strengthen "this plan is unlikely to reduce the incidence of smoking-related illnesses." "non-smoking adults"? We are worried about smokers who still smoke. Out of scope.
(B) most cigarettes currently sold in Normark contain somewhat less than the maximum amount of nicotine permitted by law. - The argument talks about reducing by 50%, and this option talks about "somewhat." It can be 1% less than the maximum or 20% less, but a 50% reduction is still an advantage. Good distortion.
(C) Inexpensive, smoke-free sources of nicotine, such as nicotine gum and nicotine skin patches, have recently become available in Normark. - This is out of scope. As our scope is limited to the effect of Nicotine and health issues related to smoking. How is it even related to the scope of the argument, which is to strengthen "this plan is unlikely to reduce the incidence of smoking-related illnesses." If we become too obsessed with this option, make a lot of assumptions, and somehow reach a conclusion that it can help reduce smoking side effects, then, at best, this is the opposite of what we are looking for.
(D) Many smokers in Normark already spend a large proportion of their disposable income on cigarettes. - At best, if they can't buy more, then nicotine side effects may be reduced, and it'll weaken the conclusion. We are looking for a strengthener here and not a weakener.
(E) The main cause of smoking-related illnesses is not nicotine but tar in cigarette smoke. - So, as people consume more boxes, they inhale more tar, they harm their health, and the plan fails, which strengthens the conclusion.