单项选择题

The discovery of the Antarctic not only proved one of the most interesting of all geographical adventures, but created what might be called "the heroic age of Antarctic exploration". By their tremendous heroism, men such as Shackleton, Scott, and Amundsen caused a new continent to emerge from the shadows, and yet that heroic age, little more than a century old, is already passing. ①Modern science and inventions are revolutionizipg the techniques of former explorers, and, although still calling for courage and feats of endurance, future journeys into these icy. wastes will probably depend on motor vehicles equipped with caterpillar(履带式车辆) traction rather than on the dogs that earlier discoverers found so invaluable.
Few realize that this Antarctic continent is almost equal in size to South America, and enormous field of work awaits geographers and prospectors. The coasts of this continent remain to be accurately charted, and the mapping of the whole of the interior presents formidable task to the cartographers who undertake the work. ②Once their labors are completed, the vast natural resources which scientists believe will furnish one of the large treasure hoards of metals and minerals the world has yet known, an almost inexhaustible source of copper, coal, uranium, and many other ores will become available to man. Such discoveries will usher in an era of practical exploitation of the Antarctic wastes.
③The polar darkness which hides this continent for the six winter months will be defeated by huge batteries of light, and make possible the establishing of air fields for the future inter-continental air service by makjpg these areas as light as day. Present flying routes will completely change, for the Antarctic refueling bases will make flight from Australia to South America comparatively easy over the 5,000 miles journey.
The climate is not likely to offer an insuperable problem, for the explorer Admiral Byrd has shown that the climate is possible even for men completely untrained for expeditions into those frozen wastes. Some of his party was men who had never seen snow before, and yet he records that they survived the rigors of the Antarctic climate comfortably, so that, provided that the appropriate installations are made, we may assume that human beings fi’om all countries could live there safely. Byrd even affirms that it is probably the healthiest climate in the world, for the intense cold of thousands of years has sterilized this continent, and rendered it absolutely germfree, with the consequences that ordinary and extraordinary sicknesses and disease from which man suffers in other zones with different climates are here utterly unknown. ④There exist no problems of conservation and preservation of food supplies. for the latter keep in definitely without any signs of deterioration; it may even be that later generations will come to regard the Antarc as the natural storehouse for the whole world. Plans are already on foot to set up permanent bases on the shores of this continent, and what so few years ago was regarded as a "dead continent" now promises to be a most active center of human life and endeavor.
The most healthy climate in the world is ______.