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1. The researchers found that the threshold substances for this reaction were very low.
研究人员发现，这个反应的门槛物质非常低。
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2. The scientists have identified several threshold substances that could potentially lead to a new breakthrough.
科学家们已经识别出几种可能引发突破性的门槛物质。
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3. The study revealed that the threshold substances for detecting pollution in the air were quite small.
研究显示，检测空气中污染的门槛物质非常小。