Given the task definition and input, reply with output. In this task, you will be shown a conversation. You need to write a question with three choices for the conversation. Your question should be answerable based on the conversation and only have one correct answer. Note that you don't need to answer your question. "W" and "M" in the conversations stand for "woman" and "man".

M: Everyone seems to be on a diet nowadays. Have you noticed that? W: Everyone seems to talk about that, especially girls. M: A friend of mine was on a sweet potato diet. He ate a sweet potato for breakfast, a sweet potato for lunch and another one for supper. W: That's bad for his health. Has he lost any weight? M: Yes. But he didn't last long. One day he felt sick and was sent to hospital. The doctor had to keep him there for a week. W: I'm very sorry to hear that. I think if you want to lose weight, you should not eat too much but you have to eat all kinds of food, vegetables, fruits etc.. And you should also do more exercise. M: I agree with you.
What are they talking about? (A) A story about a friend who was on a sweet potato diet. (B) How to keep diet. (C) People should eat all kinds of things.