修建中国长城的工程跨越了数千年。其中最著名的部分是明朝时期建造的蜿蜒的防御工事,建于14世纪至17世纪之间。它每年吸引着上千万的游客。与之相比,已有2000年历史的汉代长城——如今看起来有点像是堆放在沙漠中布满灰尘的饼干——吸引的游客要少得多。
Multi-annual measurements across Lake Superior indicate remarkable similarities between large lakes and ocean CO2 exchange during the ice-free season.
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