#25 - Global Reference, Must Be True

[Administrator]

Please post below with any questions!

[wrjackson1]

Hi, could elaborate on answer choice C? I chose it thinking that if CFC is such a big problem, then they would also regulate other chemicals that would release chlorine in the upper atmosphere. I'm not sure if I'm misinterpreting the information or making unwarranted assumptions

[James Finch]

Hi WR,

This passage describes the gradual scientific understanding and acceptance that CFCs in the atmosphere ultimately lead to the destruction of the ozone layer. The passage describes how this process occurs, and how it came to be understood, but does not talk criticize this understanding or point to other possible causes for ozone layer depletion. Answer choice (C) would seem to be reasonable because CFCs are the only thing mentioned that deplete the ozone layer, and they do so by breaking down when exposed to ultraviolet light and releasing carbon into the ozone gas, which then reacts with the ozone and breaks down the ozone.

The immediate red flag with this answer choice, however, is its simultaneously broad and vague nature: "few chemicals," "can", etc. In order to logically conclude this, we would have have to have been given information about the entire range of chemicals in existence and how many of them break down into chlorine. We don't have that information, so we can't logically draw (C) as a conclusion.

Answer choice (D), however, connects logically to the link between ultraviolet light and skin cancer, ozone blocking the UV light, and CFCs leading to the breakdown of the ozone. This does require putting together disparate information scattered around the passage, but this common for Reading Comprehension Must Be True questions, so it's good practice to get in the habit of making those linkages while reading the passage.

Hope this helps!

[meercat44]

I'm really struggling to see how D is correct here. The only mention of skin cancer that I can see is at the very top - that it's well established that UV light contributes to skin cancer - but wouldn't it be sort of a cause/effect stretch to say that regulating CFCs can reduce skin cancer incidences? What if, once the damage to the ozone layer has been done, there's no way to lower the incidences of skin cancer? The evidence in the passage felt really thin to me here...I put A as my answer, but none of them really felt right to me.

[James Finch]

Hi Meerkat,

The causal linkage that this question is asking test takers to make is:

More CFCs Less Ozone More UV More Skin Cancer

Assuming all other things being equal, as an indirect cause it does make sense to infer from the passage that:

Fewer CFCs More Ozone Less UV Less Skin Cancer

This is based on an assumption, as you note, that there still is an ozone layer, but based on reading the totality of the passage this is a fair assumption to make.

We can contrast this to (A), which is completely unsupported by the passage. We know that chlorine released by CFCs destroys ozone, but we have no idea from the passage how the ozone layer is naturally maintained/destroyed.

Hope this helps!

[James Finch]

Hi Meerkat,

The causal linkage that this question is asking test takers to make is:

More CFCs Less Ozone More UV More Skin Cancer

Assuming all other things being equal, as an indirect cause it does make sense to infer from the passage that:

Fewer CFCs More Ozone Less UV Less Skin Cancer

This is based on an assumption, as you note, that there still is an ozone layer, but based on reading the totality of the passage this is a fair assumption to make.

We can contrast this to (A), which is completely unsupported by the passage. We know that chlorine released by CFCs destroys ozone, but we have no idea from the passage how the ozone layer is naturally maintained/destroyed.

Hope this helps!

[RajPatel]

Can someone elaborate on answer choice A being incorrect? The explanation is that this is contradicted by lines 11-14 in the passage, which state "In the absence of pollutants, stratospheric ozone concentrations should remain stable over time, with natural production and destruction of the gas in rough equilibrium."

However, answer choice (A) has the words "little or no ozone destruction," not just none, and lines 11-14 in the passage do not specify how much or how little production and destruction of the gas in rough equilibrium occurs. I believe it would make more sense for (A) to be incorrect if it instead used the words "No ozone destruction occurs naturally in the stratosphere unless chlorine is present."

[Adam Tyson]

For a Must Be True/Most Strongly Supported question like this one, RajPatel, don't focus on trying to disprove the answer. Instead, look for evidence that DOES support it. Is there any evidence in this passage that there is little or no natural destruction of ozone? We know it's not zero because of those lines you cited. Where in the passage is there evidence that there is little such destruction? Don't treat this as a Could Be True question - we aren't looking to see if this answer is possibly true. It's possible, but is there any support that would lead us to conclude that it is true? I find none.

It's not that answer A is "incorrect." It's that there is no reason to infer it, and so it is not an acceptable response.