Although there is 34,500 tons of gaseous nitrogen in the air column above each acre of the earth's surface, this cannot be used by plants until it has been fixed by nitrogen-fixing bacteria and algae.

虽然在地球表面每英亩空气柱中有34,500吨气态氮，但是如果这些气态氮不被固氮菌和藻类固定，是不能被植物利用的。

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The total annual expenditures is equal to the sum of the main categories only (in this particular case subcategories cannot be used since they are not comprehensive).

FORBES: Visualizing the Table of the Graph Makeover Contest

Admittedly, this is more complex than plurality voting and cannot be used with current American voting machines (though it is used in Australia).

ECONOMIST: The mathematics of voting

The threat of an EMP attack is hardly the only reason for ensuring that ballistic missiles cannot be used to do harm to this country, but it is a particularly compelling one.

CENTERFORSECURITYPOLICY: The terror next time