PrepTest 146

Incorrect. (Lines 12-14) This is a tempting answer since it's CFCs and chlorine that are said to lead to the depletion of the ozone layer! However, this answer is about natural destruction of the ozone layer, not natural depletion. And the passage states that there's a natural equilibrium—ozone forms as quickly as it's destroyed. As such, naturally, there is ozone destruction, but it's balanced out by ozone creation.

Incorrect. (Lines 1-2) The passage notes that UV radiation contributes to skin cancer. However, it doesn't compare it to other causes of skin cancer, so we can't pick this answer about it being a primary cause. Additionally, we don't know the mechanism by which UV radiation causes skin cancer—it might not be because of excessive absorption.

Incorrect. The passage doesn't discuss chemicals other than CFCs, so this answer is out of scope. While you might reason that if there were other chemicals that could release chlorine, then the ozone would have been depleted before CFCs were in wide use, that's bad reasoning—maybe those other chemicals are extremely rare and thus don't contribute much chlorine.

Correct. Question Type:
Must Be True

Strategy Overview:
Head straight to the answer choices and use our notes and the passage to find the correct one

Answer Anticipation/Relevant Lines:
Similar to Question #23, the question stem here gives no guidance as to the topic of the correct answer, so we shouldn't spend a lot of time anticipating what will be correct. Instead, we should head straight to the answers and focus on the ones that line up with our overall understanding of the passage. From there, we can use our notes and the passage itself to check that answer.

Answer Explanation:
(Lines 3-6; Lines 26-28) This answer relies on a lot of causality in the passage, which is something that we should generally be tracking. We know that UV radiation causes skin cancer. We know that the ozone layer blocks UV radiation. And we know that CFCs deplete the ozone layer. As such, regulating CFCs would prevent the depletion of the ozone layer, resulting in more UV radiation being absorbed by it, and thus less UV radiation reaching humans and causing cancer. This answer is therefore supported by the stimulus, so it's the correct answer.

Key Takeaway:
Science passages are frequently about causal relationships. Be sure you at least note the general causality presented in the passage, even if you don't track each intervening step. Here, knowing that UV radiation causes cancer, the ozone layer causes less UV radiation to reach Earth, and CFCs cause the ozone layer to get depleted would have been enough to answer the question, without needing to track the individual steps of how CFCs cause damage outlined in Paragraph 2.

Incorrect. (Lines 51-53; Lines 21-28) The hole in the ozone layer over Antarctica was noted as the vindication of M+R's views. However, the passage doesn't state that the depletion of the ozone layer accumulates where the CFCs flow upwards. It's possible that the damage to the ozone layer happens all over, but then for some reason it aggregates over Antarctica.