what had happened happened again,这句语法对么,或者怎样改,

题目

what had happened happened again,这句语法对么,或者怎样改,

答案

时态和句型上都是正确的
what had happened是本句的主语从句 happened 是谓语动词
由于谓语动词用的过去式 所以主句应该是过去的过去用过去完成时 正确