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?
(A) Extraterrestrial influences on the ozone layer
tend to occur less often than terrestrial ones.
(B) Natural events, such as the eruption of
volcanoes, continue to damage the ozone layer
today.
(C) Our earliest ancestors possessed genetic
characteristics making them more resistant than
we are to the harmful effects of ultraviolet
radiation.
(D) The ozone layer regenerates at a slow rate,
barring counteractive processes.
(E) Scientists have discovered that genetic changes
occurred in our ancestors during the period in
which the supernova affected Earth.
[spoiler]OA:C[/spoiler]
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?
(A) Extraterrestrial influences on the ozone layer
tend to occur less often than terrestrial ones.
(B) Natural events, such as the eruption of
volcanoes, continue to damage the ozone layer
today.
(C) Our earliest ancestors possessed genetic
characteristics making them more resistant than
we are to the harmful effects of ultraviolet
radiation.
(D) The ozone layer regenerates at a slow rate,
barring counteractive processes.
(E) Scientists have discovered that genetic changes
occurred in our ancestors during the period in
which the supernova affected Earth.
[spoiler]OA:C[/spoiler]
Life is Tom; I am Jerry 
