假如主句中是过去时的话,一般间接引语是要改成过去完成时,表示过去的过去
比如：He said: " I visited my grandma yesterday."
改成间接引语就是：
He said that he had visited his grandma the day before.
这里,visit 这个动作是发生在say 之前,所以要用过去完成时,表示过去的过去.