We have a lot of invitation cards, but they are all for the same date.
我们接到了许多请帖,但是上面的日期却全都是同一天。
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。