He said"I visited the Great Wall in 2001."改为间接引语He said that he

过去完成式是不能单独用的.我们用的时候必须有另一个事件.比如说,有两件事:A和B,两件事都发生在过去,但A发生在B之前,那麼A用去完成式,B则要用过去式,如:
He had worked before he decided to go to college.他念大学以前曾工作过.
你的句子:He said " I visited the Great Wall in 2001." 是表示过去某个时间做过的事,是要
用一般过去式的.(这是一个直接陈述句,若是间接转述句,就会用到过去完成式了,因为他去参观长城是在他说话之前发生的动作,句子是:He said that he had visited the Great Wall before.)
清楚了吗?那改为间接引于是He said that he had visited the Great Wall in 2001. 还是He said that hevisited the Great Wall in 2001後者