它既能自然合成，也可通过生物化学家人工合成。
They occur naturally but biochemists can make synthetic versions.
胆固醇是由人体自然合成的脂肪物质，很多食物中也含有胆固醇。
Cholesterol is a fatty substance made naturally by the body and also found in many foods.
我们试过合成的和自然的纤维，我们想知道不同的纤维分解有多快。
We tested synthetic and natural fibres; we wanted to know how fast different fabrics decompose.
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