题目

图甲是凸轮开关外形，挡位“2”、挡位“1”与挡位“0”的夹角均为45°；图乙是开关旋至不同挡位时，触头的开闭情况。下列设计的凸轮形状中，最合理的是（ ） A . B . C . D . 答案：D—It was such a difficult examination that a lot of students were unable to finish it on time.—That's the case. It's hard to accept the fact that over 90% of my classmates ________.A.should failB.should have failedC.will failD.may fail