A、Because some people don’t think they need the sun to get vitamin D. B、Because it’s an example of an evolutionary compromise. C

M: Can wearing sun glasses make you more vulnerable to sunburn? Are there people who can resist the AIDS virus better than others? Can a human body rust to death? In his new book Survived of the Sickest, a Medical Maverick discovers why we need disease. Sharon Moalem explores these and other medical mysteries. Sharon, nice to see you, good morning. Let me dare say, you are an evolutionary biologist and a neural geneticist.
W: That’s right.
M: What is that and why does it make you look at things from different points of view?
W: Well, the evolutionary biologist part, it allows me to understand how our ancestors essentially influence who we are today. So whatever they experienced, be it a plague or a climate change, they adapted, they survived, and they passed down those adaptations to us like skin color or disease.
M: So let’s take a look at this question of "is it possible for people to actually rust to death?" Medically speaking, is it possible?
W: Yes, thank you for asking that question. Ah, it is. Over a million Americans might be at risk from too much iron. Today you absorb too much iron from the diet, and it essentially gets into certain organs and over time can rust them. So if it’s in the liver, it can cause liver cancer.
M: You actually suffer from this.
W: Right.
M: So, this, and the treatment for this sounds a bit barbaric.
W: Well, it’s amazing actually. It’s a simple blood donation.
M: But it’s basically bleeding someway.
W: Right.
M: Well, you’re getting rid of the iron-rich blood so that it can build up slowly again over time.
W: Right.
M: Alright. The second idea, sun exposure, skin disease experts everywhere are gonna be shocked when they hear this, because they say "stay out of the sun, no matter what". And you say "a certain amount of sun exposure actually can make us healthier".
W: Right, essentially, we need vitamin D, so we evolve to convert cholesterol into vitamin D. Those are a few steps to get it and Vitamin D is not just good for the bone, it’s good for the immune system. So take African-Americans for example, who live in the northeastern United States, they’re at higher risk for prostate cancer than their cousins in Florida. And the reason for this is they don’t get enough sun.
M: And another example: the cholesterol levels in people tend to go up in the winter.
W: That’s right.
M: Because you’re not breaking down the cholesterol into vitamin D in the same levels.
W: Exactly.
M: Alright. But this is very individual. You shouldn’t just tell everybody "go out and get in the sun".
W: Oh, no, no. And again this is an example of an evolutionary compromise. You shouldn’t get too much sun, but you still need the sun.
Questions 1 to 5 are based on what you have just heard.
1. Why is it possible for people to rust to death?
2. What is the treatment of diseases related to rusting?
3. Why does Sharon think moderate sun exposure makes people healthier?
4. Why are people likely to have a higher cholesterol level in winter?
5. Why shouldn’t everybody go out and get in the sun?