be unknown;unable to find out; not know ❍ 我当时是否也如K委员长似的眉头打结呢，未曾照镜，～。(《鲁迅选集》Ⅲ—23) Whether I also frowned like Commissar K or not I do not know,for I did not look in the mirror. ❍ 至于 “克米阿派忒拉”之类，总长看了没有，我可～了。(《鲁迅《华盖集续编》142) Whether the minister had read Cleopatra and the other books or not I do not know.
不得而知bù dé ér zhī
得：能够。形容无法知道。cannot know sth.,can make nothing of it,unknown, not know