题目

--- How do you learn English？ --- I learn English by _________. A. listen to tapes            B. speak it as much as possible   C. listening to tapes            D.ask the teacher for help 答案：C到我省迪庆州梅里雪山旅游时，有的人常常会感到呼吸困难，这是因为空气成分中（ ）A．氧气的体积分数远大于2l%B．氮气的体积分数远小于78%C．氧气的体积分数仍约为21%，主要是由于高原空气稀薄D．二氧化碳的含量太高