类地行星主要是岩石：密度大的石块和金属物质，同时会有少量的气体。
The terrestrial planets are mostly rocks: dense rocky and metallic material, with minor amounts of gases.
收割下来的枝叶会将有毒的化合物转移到远离这片区域的地方，它们将被焚烧或者用作堆肥，回收金属物质用于工业用途。
A harvest of the shoots would remove the toxic compounds off site to be burned or composted to recover the metal for industrial uses.
交通污染物质中往往含有更多的金属物质，可能在肺部产生有害的自由基。
Traffic pollution tends to contain more metals, which react to produce damaging free radicals in the lungs.
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