1. We live in the twentieth century.
    我们生活在二十世纪。

2. The twentieth century is the century of planetary overcrowding.
    20 世纪是地球上人口过度拥挤的不安定的世纪.

3. The twentieth century is the century of planetary overcrowding.
    20 世纪是地球上人口过度拥挤的不安定的世纪.

4. The door man said, "You must go to the twentieth floor."
    看门人说："你们必须上20楼。"

5. The twentieth century began with powerful countries competing to take advantage of the Earth.
    从20世纪初起，各强国竞相利用地球资源。

6. Audiences in the second decade of the twentieth century found
    生活在20世纪20年代的观众认为，

7. A man without an education, many of us believe, is an unfortunate victim of adverse circumstances, deprived of one of the greatest twentieth-century opportunities.
    我们许多人都相信，一个没有受过教育的人，是逆境的牺牲品，被剥夺了20世纪的最优越的机会之一。