写字楼物业治安要定期检查办公楼的安全设施，监控室要( )小时有人监控。
A．8
B．12
C．24
D．48
参考答案：C
（）是指实际焦点在射线发射方向上的投影面积。
After the long march, the troops reached their destination, ____________.
A．hungry and friendly
B．hungry and tired
C．hungrily and tiredly
D．hungrily and tired
