煤是由埋在地底的森林经过长期而缓慢的化学变化过程而形成的。
Coal was formed out of dead forests by a long slow process of chemical change.
但是，很多有效成分会在烹调过程中发生化学变化而降低，甚至是丧失其功效。
However, a lot of valid composition will lose their effect in cook process.
但是，很多有效成分会在烹调过程中发生化学变化而降低，甚至是丧失其功效。
However, a lot of valid composition will lose their effect in cook process.
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