In the 20th century the main threat to international security was superpower conflict.

在20世纪，对国际安全的主要威胁是超级大国的冲突。

In the 20th century, it was totalitarianism.

在20世纪是极权主义。

But in the 20th century, something unexpected happened.

但在二十世纪，料想不到的事情发生了。

It was built in the latter part of the 19th century and the early part of the 20th century.

它建于19世纪后期，20世纪前期。

It remained in widespread use until late in the 20th century.

在20世纪末之前，它仍然广泛使用。

We listen to music in the 21st century in a profoundly different way than we did in the 20th century.

在21世纪，我们听音乐的方式与20世纪相比已有天壤之别。

Modernism became popular in the early part of the 20 th century.

现代主义在20世纪初开始流行起来.

The steam engine in the middle of the 19th century, the mass-production model in the beginning of the 20th century, thanks, Mr. Ford.

它们分别是：19世纪中叶的蒸汽机，20世纪早期的大规模生产模型——这要感谢福特先生。

In fact in the second half of the 20th century growth was even higher than anything you would have predicted based upon the first half of the 20th century.

事实上，20世纪下半叶的增长速度远远超过了任何预测，如果你的预测是基于20世纪上半叶的数据。

The steam engine in the middle of the 19th century, the mass-production model in the beginning of the 20th century -- thanks, Mr. Ford.

它们分别是：19世纪中叶的蒸汽机，20世纪早期的大规模生产模型--这要感谢福特先生。