改错并指出错误I wanted to know whether have they been to the Great

I wanted to know whether they had been to the Great Wall
我这样改的原因是：
1、关于have been顺序的调整
这是因为在whether 后用陈述语序,而不用疑问语气.
更多例子：I don't know whether he can do it.我不确定他是否能完成
2、关于have 变成had
由于主句是wanted,已经表示了过去的时态,而又在讨论他们在我wanted to know这一过去动作之前,是否去过长城,过去的过去用过去完成时.