Many seeds require a period of stratification, exposure to low temperatures for some minimum period, before they will germinate.

许多种子在发芽前需要一段时间来分层，并在低温下储存一段时间。

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Between 1645 and 1715 almost no sunspots were observed, a solar period which came to be called the Maunder Minimum.

1645年到1715年间，几乎没有任何太阳黑子活动被观察到，这种时期即是所谓的。

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There is evidence that low solar activity increases their numbers , and the sun is currently in a period of minimum activity.

有证据证明太阳活动不足会增加其发生的数量，而目前太阳正处于最低活动期。

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James Ferguson, 30, formerly of Tranent, must serve a minimum period of two years and three months in prison.

BBC: James Ferguson jailed for string of attacks in East Lothian

So the seven-year stipulation isn't a requirement to automatically repeat the exercise, but a minimum period which must elapse between border polls.

BBC: United Ireland border poll call: diversions and u-turns

Free travel privileges can be withdrawn for a minimum period of six months for consistent bad behaviour like bullying or using threatening language.

BBC: London's free travel 'earn back' scheme is praised