A difficult period in human thought over and done with.

人类史上一个反复想过又抛弃了的困难时期。

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This is a difficult period for millions of American families.

对数百万美国家庭来说，现在是困难时期。

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In the most difficult period of his life, Cai Wei had to give up study.

在最困难的时候，蔡伟不得不放下书本。

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He said the most difficult period of the trip was crossing the Yukon Arctic and the Arctic National Wildlife Refuge in Alaska.

VOA: special.2011.03.23

Internet industry was in a very difficult time at that time, at that period, and we gradually realized that this company cannot really survive if we stick with the backend technology providers thing.

当时互联网行业正处于困境，如果坚持做后台搜索技术提供商,这个公司将无法生存。

斯坦福公开课 - 百度CEO李彦宏演讲：全球最大搜索引擎的发展课程节选

Now,that has changed, for sure; but,the centralization of the French government and the domination of Paris over the life of the nation is very difficult to change, over a long period of time.

现在,情况已经发生了改变,但是法国政府的中央集权化,以及巴黎在国民生活中的支配地位,在相当时间段内,都很难得以改变

耶鲁公开课 - 1871年后的法国课程节选

The Welsh government's culture minister has pledged to support the library at a "difficult period".

BBC: National Library of Wales reopens to the public after fire

Apple is transitioning from being a hyper-growth company, which has been a difficult period for investors.

FORBES: Apple: Here's Why Holders Should Be Rooting For Buybacks

And I think that that's going to be a very difficult period for Zimbabwe.

BBC: News Online