题目解析：
【题目翻译】根据第5段，南美大鲵巢穴山脊隧道内的空气会发生什么变化？
A：随着水蒸气扩散到隧道里，天气变得更加潮湿。
B：它失去二氧化碳，获得氧气。
C：它通过壁上的毛孔到达巢穴的内部。
D：它和巢巢穴心的空气方向一样。
【判定题型】：题目问的是文章中的具体细节信息，故根据题目问法可以判断本题为事实信息题。
【关键词定位】：根据关键词“in the ridge tunnels”,定位到Passage5第9句，原句为“Gases, mainly oxygen coming in and carbon dioxide going out, easily diffuse into or out of the ridges, since their walls are thin and their surface area is large because they protrude far out from the wall of the mound. ”，意思是“气体，主要是氧气进入和二氧化碳排出，很容易扩散到山脊或从山脊扩散出去，因为它们的壁很薄，而且它们的表面积很大，因为它们从山丘的壁向外突出。”。
【逻辑分析】说明氧气进入，二氧化碳排出。
【选项分析】
A：二氧化碳没有失去，只是扩散出去。错误。
B：对应选项中：It loses carbon dioxide and gains oxygen。正确。
C：原文没有提到巢穴，错误。
D：没有提到巢穴，错误。
But how is this well-insulated nest ventilated? Its many occupants require over 250 quarts of oxygen (more than 1,200 quarts of air) per day. How can so much oxygen diffuse through the thick walls of the mound? Even the pores in the wall are filled with water, which almost stops the diffusion of gases. The answer lies in the construction of the nest. The interior consists of a large central core in which the fungus is grown, below it is “cellar” of empty space, above it is an “attic” of empty space, and within the ridges on the outer wall of the nest, there are many small tunnels that connect the cellar and the attic. The warm air in the fungus gardens rises through the nest up to the attic. From the attic, the air passes into the tunnels in the ridges and flows back down to the cellar. Gases, mainly oxygen coming in and carbon dioxide going out, easily diffuse into or out of the ridges, since their walls are thin and their surface area is large because they protrude far out from the wall of the mound. Thus air that flows down into the cellar through the ridges is relatively rich in oxygen, and has lost much of its carbon dioxide. It supplies the nest’s inhabitants with fresh oxygen as it rises through the fungus-growing area back up to the attic.
