Winter closes in and the temperature drops below freezing.

冬天来临，气温降至冰点以下。

《柯林斯英汉双解大词典》

If the temperature drops below zero degree, water will turn into ice.

如果气温降到零度以下，水就会结冰。

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At night the temperature drops below zero.

气温在夜里降到零度以下。

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If the temperature drops below a certain level it sends a signal, 'turn on the heat', and that signal stays on until it gets a negative signal to turn off.

如果温度降到一定程度以下时,探测器会发送一个信号,打开加热器,直到加热器再收到关闭的信号,它就会一直开着

耶鲁公开课 - 生物医学工程探索课程节选

When the body's core temperature drops below 95 degrees Fahrenheit, a mild form of hypothermia takes hold.

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