如果“它们”存在——本文的前提是假设它们确实存在——那么到底有多少外星文明，能让我们期待与之相遇呢？

If "they" are out there — and for the purpose of this article let's assume they are — then how many alien civilizations can we expect to come across?

youdao

中印两国交往历史之久远、影响之深刻，在世界文明史上实属罕见。

The long history and deep impact of intercourse between the two countries are rare in the history of world civilization.

youdao

余曾试图明示，美国人民乃无任何文明之民族，盖因其甚为年轻，不够渊长。

The American people, I have tried to show, are still a nation without any civilization and that is because they are still a young nation.

youdao

The civilization of the West, however, was not the result of some inevitable process through which other cultures will automatically pass.

然而,西方文明的发展之路,并非经历了其他文明必经之途中,一些不可避免的发展过程

耶鲁公开课 - 古希腊历史简介课程节选

All the goods of civilization, Hobbes tells us, stem from our ability to control pride.

霍布斯告诉我们说，文明之所以文明，源自于我们对追求荣誉之心的克制。

耶鲁公开课 - 政治哲学导论课程节选

It was a civilization that was rather advanced in terms of its agricultural skill.

这是一个文明,在农业技艺方面先进之所在

耶鲁公开课 - 古希腊历史简介课程节选