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@PythonDvz B. list1 is appended into itself but Python needs to represent the reference to itself with ellipses (...) to prevent an infinite loop.
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@PythonDvz After appending list becomes recursive list, so python prints B option.
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@PythonDvz I was to offer A as an answer, but I realized I had confused append() with extend(). Append adds list1 to itself as an element, creating a recursive structure (B).
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