听力原文：W: May I help you, sir？
M: Er, I'm wondering how much this book is.
W: There's a price tag on the back page of each book. Have you seen it？
M: Yes, I saw it. But I just can't believe my eyes. Is it really ＄65？
W: Well, I'll check it through the scanner…Yes, it's ＄65.
M: Wow! That's a lot of money for a book.
W: Yes. Medical texts are usually very expensive.
M: Well, I regret choosing medicine as my major now. If I knew this earlier, I might choose to learn mathematics or something else. W : Really？
M: No, not really. I'm joking. I love medicine and hate mathematics. Although this book is quite expensive, I have to have it.
W: How would you like to pay for it, in cash or by credit card？
M: In cash. W: That'll be ＄ 70.36.
M: But you said it was ＄ 65.
W: Well, with tax, it comes to ＄ 70.36, sir.
M: There's a tax even on books？
W: I'm afraid so.
M: All right, here are two fifties.
W: Here's your change, sir. It's ＄29.64.
M: Thanks.
W: Have a nice day.
Why didn't the man believe his eyes？

A. Because he didn't know the price.
Because he didn't see the price tag.
C. Because medical texts are usually expensive.
D. Because the price is too high.