运输机械按照用途、结构形式、工作原理等，可分为（）。
A.输送机械
B.提升机械
C.给料机械
D.装卸机械
参考答案：A, C, D
工件对比度受试件厚度差影响（）。
Bob insisted that he_______nothing wrong and _____ from work. [ ]
A. did; won't be fired
B. had done; not be fired
C. should do;mustn't be fired
D. do; shouldn't be fired
