It should be noted that the central idea simply means the main, unifying element that can be found in the story.
Your information is incomplete as you didn't given the part A of the passage. Therefore, an overview will be given. The central idea is the main idea that's in the story.
In this case, it's important that to know the central idea in part A. This is the dominant impression that's found in the story. Then, it'll be easier to find the evidence that supports the central idea.
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