We don’t care about other influences on the ozone layer; the argument is specifically focused on whether or not damage to the ozone layer caused by CFCs will be harmful for humans. Furthermore, the quantity of these extraterrestrial influences definitely isn’t relevant.

Similar to (A), for this argument, we only care about the impact that CFCs have on the ozone layer; other influences on the ozone layer are irrelevant to the commentator’s argument.

(C) widens the gap between the premises and conclusion. It’s great that our earliest ancestors weren’t harmed by the damage to the ozone layer, but if they were more resistant than we are to UV radiation, then we cannot use their experience as a basis for this claim about humans.

The argument is about damage to the ozone layer, not repairing the ozone layer, so this is outside of the scope of the argument. We don’t know if any counteractive processes are happening.

This is too vague––without any indication of what kind of genetic changes occurred, this is not enough information to weaken the argument. It could be the case that all of these genetic changes are completely independent from reactions to UV radiation.