when I reached home,my parents _ their supper.A.are having B.have already hadC.have had D.had already had为什么不选B而选D?

when I reached home,my parents _ their supper.A.are having B.have already had
C.have had D.had already had
为什么不选B而选D?

因为reached 是过去式 他们在我到家之前就吃完了 所以是过去的过去 所以是过去完成时 而不是现在完成时

had already had过去完成时，我reached的动作之前发生，过去的过去。had +done。而Bare having不是过去时态

因为前面的reached就是一个过去时
如果是reach 现在时 就可以选b