题目

What is the probable relationship between the speakers?A. Colleagues B. Brother and sister C. Teacher and student 答案：【答案】A【解析】此题为听力题，解析略。自然界中植物的光合作用需要消耗空气中的 A．氮气         B．氧气             C．二氧化碳         D．稀有气体