The little bamboo tree had been growing underground for the past four years, in the fifth year and beyond, it developed a root system strong enough for its ground growth.

过去的四年里，这株小竹子一直在地下生长，第五年开始，它形成了足够强大的根系，可以在地面生长。

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Another solar system has a planet 22 times the mass of Earth, orbiting every four days, and a Saturn-like planet with a 3-year period.

另一个太阳系有一颗质量是地球22倍的行星(译者：可怜的小地球)，公转周期为4天，还有一颗公转周期为3年的类木星行星。

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For ordinary people, more obviously valuable is a four-year-old system for homeowners to assess property tax online, rather than have crooked inspectors visit their homes.

对于普通的人，最有明显价值的是一个用了4年的系统，该系统让屋主在线评估物业税，而不是让心思不正的监察员登门拜访。

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The four-year-old bitcoin payment system is among the most popular of the new methods.

WSJ: 'Virtual' Currencies Draw State Scrutiny

By and large, businesses welcomed this tidying up, even though they will pay more tax during a four-year transition to a new system of payment, under which big firms will pay tax quarterly on a current-year basis, rather than in arrears as now.

ECONOMIST: Gordon Brown’s progress | The

These schools feeds into a system of four-year universities among which are such engineering giants as Purdue University.

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