This does not affect the argument. The magnitude of the threat is not relevant to the argument, which is focused on the urgency of a threat.

This strengthens the argument. It provides support for the author’s assumption that health is not a pressing concern for most people when they quit smoking.

This does not affect the argument. (C) says some actions that make health issues worse can make social pressure better. This is not relevant to the argument, which is about what motivates people to stop smoking cigarettes (which we can’t assume is one of the actions described).

This does not affect the argument. The psychiatrist already notes that breaking a habit is difficult, and is more concerned with what motivates someone to try hard enough to succeed in breaking the habit.

This does not affect our argument, as (E) doesn’t tell us anything about how many people fall into either category. It may strengthen the argument if most people quit because of social pressure. It would weaken it if most people quit because of health concerns.