評論
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答案：A
解析：
The sentence indicates that "an onslaught of glaciers" once changed things in "northern forests" but not in "forests in the southern region of the continent." It makes sense to suggest that the forests that did not have their "flora and fauna," or plants and animals, wiped out by glaciers would be "rich in plant and animal diversity," or would contain a vast amount of different plants and animals.
