A、Drug addiction. B、A headache. C、Pain-killers. D、The woman’s suggestion. B对话中女士问男士是不是不舒服，为什么皱着眉头，男士回答说他有点头痛。可知令男士烦恼的是他的头疼，故B项正确

W: Hey, John, are you OK? Why are you frowning?
M: Well, I sort of(22)have a headache. I’ll be fine after a glass of boiled water and some pain-killers. That happens a lot, and I always take one or two of them whenever a headache occurs.
W: A lot? Seriously? Have you ever seen a doctor?
M: Of course I have. Guess what? He just told me to take some pills or let it be until the headache was gone by itself. So, I chose the first.
W: Then how did you get those pills? (23) On prescription?
M: (23)I had no choice.
W: Now I have to tell you for your own good that it will be pretty dangerous if you go on taking those pain-relievers like this.
M: How come? It’s only a kind of normal medicine, and I don’t take many each time.
W: Well, I’ve read an article that said, believe it or not, (24) although most people think pain-relievers are safe, they are in fact addictive, in the same way as heroin and morphine.  Some people even visit the doctor regularly on purpose to satisfy their addiction.
M: You must be kidding me! Does that mean I have made myself a drug addict or something? That’s terrifying !
W: Oh, don’t be scared. As long as you are aware of it and pay some attention to the dose, your doctor is not likely to appear as a "drug dealer".
M: (25) That sounds reasonable. It seems that I must take notice to these little white pills. Thank you for your information.
W: My pleasure.