问题描述：
______ parrots are native to tropical regions is unture.为什么答案是 That all 不是 All 呢
———— are kept as pets in almost every country in the world.为什么这里又应该选折Cats and dogs,而不是That cats and dogs.
———— are kept as pets in almost every country in the world.为什么这里又应该选折Cats and dogs,而不是That cats and dogs.
问题解答：
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