It took years (complete) the Qinghai-Tibet Railway. The construction workers (overcome) the most difficult engineering challenges, one of which was how to protect the delicate ecosystem. To allow the wild animals to move safely and freely in their (nature) habitat, they built thirty-three passages under the railway. To prevent damage to wetlands and grasslands, 675 bridges with a total length of about 160 kilometres (build) between Golmud and Lhasa. They even moved 140, 000 square metres of wetland to new area in order to protect its distinct ecosystem. (locate) at over 5, 000 metres above sea level, Tanggula Station is the highest railway station in the world. In locations such as this, the thin air, changeable weather and high levels of UV radiation presented perhaps the (great) challenge for railway workers. To make sure they stayed healthy, several oxygen-making stations were constructed. To protect Cuona Lake construction waste, the railway workers used thousands thousands of sandbags to build a twenty-kilometre wall along the lake. In a word, the railway workers built our "impossible" railway with the care that the environment deserves. It (true) is an extraordinary "Sky Railway".
