Not necessary, because although being willing to change is a necessary condition for happiness, that doesn’t imply people who meet that condition have a greater than 50% chance of obtaining happiness. You can also think about (A) through negation. If people who are willing to change do NOT have over a 50% chance of obtaining happiness, that doesn’t weaken the argument, because it can still be the case that being dissatisfied with oneself gives you a better chance of being willing to change than being accepting of oneself.

Necessary, because if it were not true — if people who are not dissatisfied with themselves are EQUALLY or MORE likely than those who are dissatisfied to pursue personal excellence — then we have less reason to think that self-acceptance is a bad thing for producing a society with happy people. Put more simply, the author assumed that being dissatisfied is better for achieving what’s necessary for happiness. But if that’s not true — if being self-accepting is just as good for achieving what’s necessary — then the author’s premise no longer supports his conclusion.

Not necessary, because the argument concerns what is more likely to cause one to “pursue” personal excellence. Whether personal excellence is ever actually obtained is a separate issue. In addition, the argument concerns the attitude of being “dissatisfied with one’s own abilities.” It’s not clear whether this implies that one “lacks genuine confidence” in one’s own abilities.

Not necessary, because the concept of being “justified” in one’s feeling content is irrelevant to the reasoning. The author never argues that a certain attitude is justified or unjustified; the argument concerns whether a certain attitude will be better or worse for achieving happy citizens.

Not necessary, because the concept of something being “painful to obtain” is irrelevant to the reasoning. The author presents a premise establishing that happiness requires pursuit of personal excellence or being willing to undergo personal change. We have no reason to think either of these involves pain.