In Rubaria, excellent health care is available to virtually the entire

Let's look at each side of the disparity discussed in the passage.

On one hand, we know that "In Rubaria, excellent health care is available to virtually the entire population, whereas very few people in Terland receive adequate medical care." In addition, "the death rate for most diseases is higher in Terland than in Rubaria." This makes sense so far -- Rubaria has excellent healthcare and a lower death rate for most diseases, while Terland has inadequate healthcare and a higher death rate for most diseases.

And here is the other side of the disparity: "the percentage of the male population that dies from prostate cancer is significantly higher in Rubaria than in Terland." So, while "the death rate for most diseases is higher in Terland than in Rubaria," the opposite is true for prostate cancer.

Our task is to find an answer choice that explains why a higher percentage of men in Rubaria die of prostate cancer, despite the fact they they receive much better healthcare than the men in Terland.

Let's first look at (B):

This tells us that men with prostate cancer are generally very old -- older, in fact, than men are expected to live in Terland. In other words, most men in Terland have already died off for some other reason before they could develop prostate cancer. In Rubaria, on the other hand, men live to a ripe old age and then develop prostate cancer. This explains why a higher percentage of Rubarian men in die of prostate cancer than do Terlandian men -- they live long enough to contract the disease. Not a very cheerful explanation, but it does explain the disparity in the passage. (B) is the correct answer.

Now look at (E):

This answer choice tells us that men who use the excellent healthcare system in Rubaria have a lower death rate than the men who do not use the healthcare system. This makes sense: the men who receive treatment have better outcomes.

However, we are trying to figure out why the death rate is lower in Terland, a place that does not have a great healthcare system -- in other words, why men who do not receive adequate treatment somehow have better outcomes (measured by percentage of men who die of prostate cancer). This answer choice does not explain the disparity at all, so eliminate (E).

I hope that helps!