It is called a sea, but the landlocked Caspian is actually the largest lake on Earth, which covers more than four times the surface area of its closest rival in size, North America's Lake Superior.
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首先理解句意是 he landlocked Caspian covers 不是 largest lake
然后根据语法规则 though这类词后面部一定是句子 可以是 V-ing/V-ed/形容词 E中 伴随状语 covering 修饰主句主语 记住 which that it 什么的都是就近修饰 就是 伴随状语 可以修饰句子逻辑主语