转述疑问句：My mum said to me,"Have you been to the Great Wall?"

My mum said to me,"Have you been to the Great Wall?" （转述疑问句）
My mum （asked） me （if） I （had） been to the Great Wall.
妈妈问我是否去过长城.
宾语从句部分是一般疑问句,用引导词if或whether连接,时态因主句而变为过去完成时.