到目前为止，我们还没有需要额外的员工，但未来可能需要。

We haven't needed extra staff ___as ___yet, but may do in the future.

到目前为止，没有救护车能够过河。

No ambulances had ___as ___yet managed to get across the river.

到目前为止，我还不知道如何解决这个问题。

I have no idea ___as ___yet how to solve this problem.