听力原文：M: Why？ Jenny？ You look unhappy.
F: I lost my temper at an old man just now, and I feel terrible.
M: Oh, you shouldn't have done that. But why did you lose your temper？
F: Lack of patience. He was counting out the coins, one by one, with his fumbling fingers. I was filled with exasperation at the checkout point. Finally, I said to him: can' t you count faster？ Not everyone has as much time as you ! he flushed. Suddenly I realized just how cruel I had been. Because I, too, could become dependent on the kindness of strangers one day when I get as old.
M: Did you say sorry to him？
F: Yes. But I just wonder, how I can become more patient. You know, when you are impatient, you are apt to be rude. And such behavior. is counter-productive, making people angry or stubborn or uncooperative.
M: Yes, I sometimes act impatiently, honking my horn the moment the light changed, speaking sharply to someone slow to understand. We really should learn various approaches for calming ourselves in stressful situations. I have even found some books to help me. There is some useful advice.
F: Can you tell me something about what you have read in those books？
M: Well, one of the books says that we should allow for marginal error.
F: What does that mean？
M: that means it is better to provide a margin for error Impatient people don't like to waste time, so they cut things too closely, For example, if you are going for an appointment, you should plan for delays.
F: Well...
Why was Jenny unhappy at the beginning of the conversation？

A. She lost some money.
B. She lost her temper and felt regretted.
C. The old man felt impatient with her.
D. She didn't have enough to do something.