空洞的良、恶性鉴别无明显意义的是（）
A.洞壁厚薄
B.洞壁形态
C.液平
D.部位
E.以上都不对
参考答案：E
— Where is John?
— Don't disturb him. He is reading a book in his study _____. [ ]
A. right away
B. right now
C. on time
D. no longer
多台小绞车接力运输，两台绞车接力处必须有（）。
A、换车场
B、车房
C、躲避峒
