题目

The conference has been held to discuss the effects of tourism ______ the wildlife in the area.        A.in B.on       C.at D.with 答案：B在汽油机的四个冲程中，都发生能量转化的一组冲程是（ ）A. 吸气冲程和压缩冲程B. 压缩冲程和做功冲程C. 做功冲程和排气冲程D. 排气冲程和吸气冲程