答案竟然已难以追查，事实上，经过几个小时的研究，我只能提前一个似是而非的理论夫妇。

The answer has been surprisingly difficult to track down; in fact, after several hours of research I can only advance a couple of plausible theories.

youdao

答案竟然已难以追查，事实上，经过几个小时的研究，我只能提前一个似是而非的理论夫妇。

The answer has been surprisingly difficult to track down; in fact, after several hours of research I can only advance a couple of plausible theories.

youdao