A、High-strength silver alloy. B、Porcelain. C、Steel. D、Iron. A本题考查推理。女士说如果通过补牙能治好男士的牙齿，她推荐男士用高强度合金牙来补牙，不要用烤瓷(porcelain)。男士回答说what

M: Hi, Dr. Hyde.
W: So, what seems to be the problems today?
M: Well, I just came in for a check up and a dental cleaning.
W: Hum. Open up. Let’s take a look…
M: Okay. Uh…
W: Hum. Wow! I’ve never seen one like this before. Let me try this.
M: Ouhhhh…
W: Well, besides a lot of plaque buildup, there is a major cavity in one of your wisdom teeth. Hasn’t this given you any trouble?
M: Well, the tooth has been bothering me, and it sometimes hurts when I drink something cold. Does it look that bad?
W: Well, we’re going to remove the decay, and then we’ll either put a filling in, or if the decay is extensive, we can’t repair it, we might have to put a crown on your tooth. Or as a last resort, we may have to extract the tooth.
M: Uh, well, that sounds painful!
W: Don’t worry. I’ve done this once before. Hah, just relax.
M: Wait! Aren’t you supposed to give me something to dull the pain?
W: I almost forgot. We can either use a local anesthetic or nitrous oxide laughing gas to minimize the discomfort you might feel. Or you can just grin and bear it.
M: No, no, no. Put me under! I can’t stand pain, and I’d rather not be aware of what’s going on. And, if I need a filling, can I get one that looks like my other teeth?
W: If we can save the tooth with a filling, I recommend a high-strength silver alloy filling instead of a porcelain one. It’ll probably last longer.
M: Okay, well, whatever. Let’s get it over with.
W: Okay, pleasant dreams.
Questions 16-20 are based on the conversation you have just heard:
16. What is the man’s initial purpose for visiting the dentist?
17. What problem does the dentist discover when she takes her first look at the man’s teeth?
18. What is the last method of treatment the dentist mentioned?
19. What kind of material will the woman use to fill the man’s tooth?
20. What method does the dentist use when extracting the decay?