一列火车长120m,匀速通过长360m的山洞,从火车进洞到车尾离洞共用1min,火车行驶是:[ ]
A.10m/s
B. 6m/s
C.8m/s
D.2m/s
答案:C
配电箱长度在()m以上时,应采用双门。
A.0.5
B.0.6
C.0.8
D.1.0
You didn't have to write the essay if you didn't want to. It was()
A.compulsory
B.suitable
C.alternative
D.optional