(1) 用单数的场合
当这些词与具体数字连用时，习惯上用单数，而且也不后接介词of。如：
He was prepared to pay two million. 他愿意支付200万。
More than a hundred people were injured. 有一百多人受了伤。
但是，当这些词后面的名词有了the, these, those等特指限定词修饰时，或其后的接的是us, them 这样的人称代词时，则此时必须用介词 of。如：
About three hundred of them have left there. 他们当中约有300人离开了那儿。

(2) 用复数的场合
当这些词不与具体数字连用，而是表示不确定的泛指数时，则不仅要要用复数，而且要后接介词of，然后才能接名词。如：
The sun was shining. Thousands of people were lying on the beach. 阳光灿烂，数以千计的人躺在海滩上。
A careless mistake cost the company millions of pounds. 一个粗心的错误使公司蒙受数百镑的损失。