what does betty think of the book ( )about harry potter?

选D
完整的句子应该是：
“What does Betty think of the book which was written about Harry Potter?”（带定语从句）
可以简化为“What does Betty think of the book written about Harry Potter?”（过去分词做后置定语）
变成第二个形式时,be动词也要省略.
因为没有which或者that,不是定语从句,排除AB
C是过去时,不是过去分词,排除.
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