You don't have to worry, we're definitely talking about trace, trace amounts.
但你不必担心，我们所说的绝对是非常，非常微量的。
They occur in such trace amounts in natural, or "whole," coal that they aren't a problem.
它们在天然煤(或称“全”煤)中仅以痕量存在，并不构成问题。
The atmosphere is roughly 78 percent nitrogen, 21 percent oxygen, with trace amounts of water, argon, carbon dioxide and other gases.
地球大气含有大约78%的氮气、21%的氧气和痕量的水蒸气、氩气和二氧化碳等其它气体。
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