Move seven feet away, and you're "close to background, " i.e., breathing normal air.
站到七尺以外的话，你已经非常接近背景水平，也就是说呼吸到正常的空气。
Effective wind protection significantly reduces the background noise of air currents.
有效的风保护极大减少气流背景噪声。
Effective wind protection significantly reduces the background noise of air currents.
有效的风保护极大减少气流背景噪声。
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