单选题：The center of a black hole is empty.

题目内容：

The center of a black hole is empty. A．Right
B．Wrong
C．Not mentioned

参考答案：【答案仅供学习，请勿对照自行用药等】

答案解析：

Black holes exist but are difficult to observe.

Black holes exist but are difficult to observe.A．Right B．Wrong C．Not mentioned

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