i'm going to go with C because ABD do not address the ancestors, which is the basis oh the whole passage. so i had it down to c and e...

IMO C

commentator’s argument is there is no reason to think that chemicals in the atmosphere harm humans in this way(by depleting ozone layers)

he supports his argument by providing evidence that a supernova greatly damaged the ozone layer, with no significant effect on our earliest ancestors.

he assumes that bcoz the ancestors were not effected by the dep of ozone layer , the claim that chemical depleting ozone layer will harm humans is wrong

but what if the ancestors non effective to dep of ozone layer is due to sme other reason like they having more resistant power , than the argument falls

which is shown by C

Commentator: Many people argue that the release of chlorofluorocarbons into the atmosphere is harming humans by damaging the ozone layer, thus allowing increased amounts of ultraviolet radiation to reach Earth. But 300,000 years ago a supernova greatly damaged the ozone layer, with no significant effect on our earliest ancestors. Because the supernova's disruption was much greater than the estimated effect of chlorofluorocarbons today, there is no reason to think that these chemicals in the atmosphere harm humans in this way.

Which one of the following, if true, would most seriously weaken the commentator's argument?

Premise : Ozone layer is damaged by chlorofluorocarbons
Damaged ozone layer allows Increased amount of ultraviolet rays on earth
Increased amount of ultraviolet rays harms humans

Counter-Premise : 300,000 years ago ozone layer was greatly damaged by supernova with no significant harm
to the human ancestors.
Damage of ozone layer was much greater by supernova than damage of ozone layer
by chloroflurocarbons

Conclusion : Estimated Harmful effects of ultraviolet radiation (damaged ozone layer) to humans is not as great as
harmful effects of ultraviolet radiation caused to human ancestors

We can weaken the argument by attacking the conclusion.


(A) Extraterrestrial influences on the ozone layer tend to occur less often than terrestrial ones.
INCORRECT : Terrestrial/Extraterrestrial influences is irrelevant.

(B) Natural events, such as the eruption of volcanoes, continue to damage the ozone layer today.
INCORRECT : Even if natural events continue to damage the ozone layer today, it does not indicate if the damage is greater than that happened during the time of our earliest ancestors.

(C) Our earliest ancestors possessed genetic characteristics making them more resistant than we are to the harmful effects of ultraviolet radiation.
CORRECT : This clearly weakens the conclusion by showing that even when the cause occurs (ultraviolet radiation) the stated effect (great harm to our earliest ancestors) does not occur.

(D) The ozone layer regenerates at a slow rate, barring counteractive processes.
INCORRECT : Regeneration of ozone layer is out of scope

(E) Scientists have discovered that genetic changes occurred in our ancestors during the period in which the supernova affected Earth
INCORRECT : Genetic changes in our ancestors during supernova time is irrelevant.[/b]

woo hoo!

A- We are talking about the effects that depletion of ozone had. So frequency matters a little.
B- In the argument, the author is talking about the harm done by chemicals, so other natural events are out of scope.
C- This option is making the thing clear that we are comparing apples to oranges. so definitely weakening.
D- Regeneration of the ozone has nothing to do with the effects of the damage.
E- this is trying to counter the premise that "There was no significant effect on our earliest ancestors". So not fit.

a definite C.

I think C is the right answer here.