OK, I think we can safely go back to notes.

好的，我想我们可以放心地继续讲下面的内容了。

麻省理工公开课 - 化学原理课程节选

And by the 1820s and 1830s the American South became what I think you could safely say was the fifth slave society in human history; maybe the sixth. This is debatable.

自十九世纪二三十年代起,美国南方,绝对成为了,人类历史上的第五个奴隶社会,也可能是第六个,这仍然处于争议中

耶鲁公开课 - 美国内战与重建课程节选

So I think I can safely say that most people had the right idea and were counting quickly, 3 though I have a feeling that some people who wrote 13 might have forgotten about those 4 f, the 4 f electrons.

我认为我可以放心地说,大部分人的想法都是对的,数得也很快，只是我感觉不少选，13，的人都是因为3,忘了，4，f，4，f，电子。

麻省理工公开课 - 化学原理课程节选