an unknown quantity

漢語翻譯

例句：

1. The new teacher is still very much an unknown quantity but we have hopes that he will be a valuable member of our team.
   新教師是誰現在還難以預料，但我們希望他會成為我們隊里的重要一員。
2. The new sales director is still a bit of an unknown quantity.
   新來的銷售部主任大家還不大了解。