With only one observation per country, it is impossible to control for unobserved heterogeneity across countries.

由于每个国家只有一个观测结果，因此不可能控制各国间未观察到的异质性。

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However, he conceded that it's impossible to control everything.

尽管如此，他承认控制一切是不可能的。

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Only the brave sell at auction, for it is impossible to control who buys or what price they will pay.

只有胆大的人才敢在拍卖行交易，因为在交易会上几乎是无法控制谁会去购买，或是他们要付多少钱。

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"The big problem is that sometimes this ball is impossible to control, " said England's Italian manager.

BBC: World Cup 2010: Fabio Capello slams 'worst ever ball'

First, they say legal immigration is impossible to control because we're a member of the European Union.

BBC: In full: David Cameron immigration speech

Recent privacy breaches of sites such as Facebook show that once information is divulged, it may be impossible to control.

CNN: Workplace rants on social media are headache for companies