任何人发现井下火灾时，应视火灾的性质，灾区通风和瓦斯的情况，立即采取一切可能的方法直接灭火，控制火势，并迅速报告矿调度室。（）
参考答案：对
18．_________a US visitor visa twice, the old couple finally gave up their hope of going to America to experience Thanksgiving Day.
A．Having been refused
B．Being refused
C．Having refused
D．To be refused
25K型客车采用（）电控制动机。
