轮对的作用机车按牵引动力可分为()、()和()。是什么?
参考答案:蒸汽机车;内燃机车;电力机车
Although metals________widely in qualities such as strength and hardness,they all have certain qualities in________.[ ]
A. vary;general
B. differ;common
C. react;particular
D. refer;detail
髓外硬膜下肿瘤X线脊髓造影表现,描述正确者为()
A.多为部分性梗阻
B.阻塞层面呈杯口状压迹
C.脊髓移位不明显
D.梗阻面呈梳状或锯齿状突然中断
E.部分阻塞时,造影剂呈对称分流