Let's return to the text for the answer here, Sophia:
In the process they tried to filter out temperature changes caused by the cyclic weather phenomenon known as the El Nino-Southern Oscillation, which warms the sea surface in the equatorial Pacific and thereby warms the atmosphere. Such warming can mask the cooling brought about by an eruption, but it can also mimic volcanic cooling if the volcano happens to erupt just as an El Nino- induced warm period is beginning to fade.
In these two lines we learn that El Nino is a cyclic warmer (answer C ), that it can mask the cooling effect of a volcano (answer B ) and can make the cooling effect of a volcano seem more pronounced (answer A). That last one is supported by the statement that "it can also mimic volcanic cooling". In other words, if a volcano erupts right around the time that El Nino is fading and not warming things up so much, the reduction in temperature that goes hand-in-hand with that fading effect might look like the volcanic eruption is making things colder. The temp was going down anyway - the volcanic eruption was just coincidentally timed with that temperature reduction.
Putting A and B together, along with the need to filter out the El Nino effect, collectively supports answer E, by the way.
I hope that helps!
Adam M. Tyson
PowerScore LSAT, GRE, ACT and SAT Instructor
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