If you can't get a cab, give me a call. It's not safe to walk home along at night.
如果你叫不到出租车的话,打电话给我,晚上一人走回家不安全。
Precautions of this sort are necessary, for it is impossible to foretell the exact nature of the difficulties which will confront the pot-holer.
作出这样的准备是必要的,因为无法预见到洞穴探险者究竟会遇到什么性质的困难。