Most biologists now accept that the tree is not a fact of nature - it is something we impose on nature in an attempt to make the task of understanding it more tractable.
现在大多数生物学家都同意，这棵树不是自然生长的——这是人类试图使理解大自然这件差事更易驾驭而强加给自然界的有价值的事物。
When one comes to more tractable land at lower altitudes, problems of permanent pasture improvement are not nearly so difficult.
在海拔较低的易于耕作的土地上，改进永久草场的问题并不很困难。
When one comes to more tractable land at lower altitudes, problems of permanent pasture improvement are not nearly so difficult.
在海拔较低的易于耕作的土地上，改进永久草场的问题并不很困难。
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