Some people are afraid of flying, which limits their options when traveling.
一些人十分害怕坐飞机,这也就限制了他们旅行时的选择了。
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。