an unknown quantity

汉语翻译

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.
   新教师是谁现在还难以预料，但我们希望他会成为我们队里的重要一员。
2. The new sales director is still a bit of an unknown quantity.
   新来的销售部主任大家还不大了解。