行车基本闭塞法分为（）、（）和（）三种。
参考答案：自动闭塞；自动站间闭塞；半自动闭塞
_________ in the mountains for a week, the two students were finally saved by the local police.
A．Having lost
B．Being lost
C．Lost
D．Losing
什么是质量管理？实施质量管理的目的？
