I know that it must be my father.过去式应该是... I knew that it must have been my father. I knew that it must be my father. 哪个对? 我一直都认为第一句must have been 是对的 但昨天我看见一句 She knew that it must be the baker.
一楼的翻译是把it当he了. 这两句都是对的,关键看你在具体语境下具体想表达的意思了. I knew that it must have been my father. 我就知道这事儿一直都是我父亲在做. I knew that it must be my father. 我就知道那是我父亲. 区别就是一个是说某事的延续,一个是说某事的时点.