264.
M: Would you please tell me about your best holiday, Nancy?
W: Well, it was my trip in Nepal. We went there 10 years ago, doing some walking in the mountains.
M: How long did you stay there?
W: 20 days.
M: 20 days! That's a long time. How far did you walk every day?
W: Perhaps 15 kilometers. You have to climb up and down a lot every day.
M: So, it was very hard.
W: Yes, very hard. Sometimes, it's difficult to walk in the mountains where the air is very thin, and you have a lot of problems when breathing.
M: What kind of equipment did you take?
W: Not much. Only a bag, a sleeping bag and some warm clothing. We carried all the things by ourselves.
M: And how was the food?
W: There was rice and some vegetables, normally no meat. But it was good.
M: What was the best thing about the trip?
W: The walking and the exercise. I hate sitting in the sun and like to be out in the countryside. The air is very clean and it's very quiet. Nepal is a good place. You must go!

答案解析：
(1) 正确答案为B。根据男子问How far did you walk every day?你们每天走多远？女子答：Perhaps 15 kilometers.大概15千米吧。可知，在旅行中他们每天走15千米，因此B项正确。
(2) 正确答案为B。根据the air is very thin, and you have a lot of problems when breathing.空气稀薄，呼吸有困难。可推知，他们遇到的问题是空气稀薄，氧气不足，因此B项正确。
(3) 正确答案为A。根据The air is very clean and it's very quiet.空气清新，非常安静。可知，女子在旅行中最享受的是清新的空气，因此A项正确。