Walden Pond is now the site of many tourist stands. It was once praised by Thoreau for its natur
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简单句(同位语结构): Walden Pond, the site of many tourist stands now, was once praised by Thoreau for its natural beauty.复杂句(定语从句): Walden Pond, which is now the site of many tourist stands, was once praised by Thoreau for its natural beauty.