It fit the environment perfectly, once they could make these things actually go twenty-five miles an hour.

它与北美的环境及其契合,人们铺路速度一度可以,达到每小时25英里

耶鲁公开课 - 美国内战与重建课程节选

That has moved around a lot, but it got almost up to 60% in the post World War II period and now it's down to less than a third.

计算所得的百分率变动很大,二战后,它一度达到将近60%,现在又降到不到三分之一

耶鲁公开课 - 金融市场课程节选