The sun emits two types of ultraviolet radiation that damage skin: UV–A, which causes premature wrinkles, and UV–B, ...

Irina on November 15, 2019

@haneenh98,

The passage tells us that sun emits UV-A radiation that causes premature skin aging, and UV-B radiation that causes sunburn. Sunscreens only protected against UV-B until about ten years ago. What can we infer from these premises?

Let's look at the answer choices:
(A) Percentage of people who wear sunscreen has increased.
Incorrect. This inference is out of scope, the premises never say anything about people's sunscreen habits.

(B) Most people whose skin is prematurely wrinkled has spent time in the sun.
Incorrect, we only know that sun radiation is one of the possible causes of skin aging, we cannot conclude that just because people experience premature skin aging, it is due to sun exposure and not another cause, and we definitely cannot infer that it is true for "most" people as (B) suggests.

(C) The specific cause of premature skin wrinkling was not known until about 10 years ago.
Incorrect. The stimulus only tells us that sunscreens did not protect against UV-A radiation until about 10 years ago, it does not mean that the harmful effects of UV-A radiation were not known. The other issue with this answer choice is that it is extremely broad - it implies that any causes of premature skin wrinkling - not only sun-related - were not known, which is entirely out of scope of the stimulus.

(D) People who wear sunscreen now are less likely to become sunburned than 10 years ago.
Incorrect. The stimulus tells us that sunscreens did not protect against UV-A rays until about 10 years ago but they did protect against UV-B rays, which cause sunburn, meaning we cannot definitively say that people today would be most likely to get burned. It is important that we avoid making any unwarranted inferences, such as that sunscreens today are more effective or people are better at following sunscreen application instructions.

(E) Until about 10 years ago, people who were sunscreen were no less likely to get premature wrinkles that people who did not.
Correct. The stimulus tells us that sunscreens did not protect against UV-A rays which cause premature wrinkles until about 10 years ago, meaning that before then, wearing sunscreen had no impact on one getting exposed to harmful UV-A rays and experiencing premature skin aging.

let me know if this makes sense and if you have any further questions.