当基本闭塞设备不能使用时,应根据列车调度员的命令采用电话闭塞法行车。
参考答案:对
Lily had a bad stomachache. But the doctor said there was ____________with her.
A.new nothing
B.serious somthing
C.everything serious
D.nothing serious
蛔虫病的主要感染途径是()
A.皮肤接触
B.经口吞入虫卵
C.经呼吸道
D.经中间宿主传播
E.以上都不是