题目

A growing number of people are beginning to believe that learning new skills and knowledge _____ more promotion opportunities. A. contributes to          B. refers to                   C. devotes to               D. appeals to 答案：A5．如图所示为内燃机工作的四个冲程示意图，其中表示压缩冲程的是（　　）A．B．C．D．