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1.The lungs are filled with tiny air sacs called alveoli, which are essential for gas exchange.
肺部充满了称为肺泡的小气囊，这是气体交换所必需的。
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2.During sleep, the alveoli in the lungs expand to allow more oxygen to reach the bloodstream.
在睡眠时，肺部的肺泡囊扩张以允许更多的氧气到达血液。
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3. In some cases, a condition called emphysema can cause the alveoli to collapse, leading to difficulty breathing.
在某些情况下，一种叫做肺气肿的状况会导致肺泡囊塌陷，导致呼吸困难。