听力原文

So far, only a fraction of China's caves have been thoroughly prospected and cavers are constantly discovering new subterranean marvels, many of which are subsequently developed into commercial show caves.
迄今为止被探索发掘的中国洞穴是中国大地上的九牛一毛，而被发掘的洞穴不断为我们展现地底奇观，许多在后来被开发成了商业景点。
Finally escaping the darkness, the cave river and its human explorers emerge in a valley far from where their journey began.
探索者沿着洞穴河流出山谷的轨迹逃离了黑暗，出现在远离出发地的河谷。
For now, the adventure is over. Rivers which issue from caves are the key to survival in the karst country.
这场冒险拉上了帷幕。源自洞穴河流为喀斯特地区提供了生命之泉。
This vertical gorge in Guizhou Province is a focal point for the region's wildlife.
贵州的垂直峡谷成为了当地野生动物的密集焦点。

重点讲解

重点讲解：
1. a fraction of
少量；小份；一点儿；
eg. The car missed me by a fraction of an inch.
那车子差一点儿就要撞到我了。
eg. The cost is only a fraction of his salary.
那项费用不过是他薪水的一小部分。
2. develop into
（使）发展成，变成；
eg. The small port has developed into a big city.
该小港市已发展成为一个大城市。
eg. With in minutes, you will see your mind map develop into a dynamic sketch.
在几分钟之内，你就会看到你的构思已经变成一幅生动的草图。
3. issue from
（液体、声音、气味）流出，发出，冒出；由于…产生；
eg. A tinny voice issued from a speaker.
扬声器里传出了细微的声音。
eg. His difficulties issue from his lack of knowledge.
他的困难是由于知识贫乏造成的。