你所要求的事情根本无法完成——那是不可能的。

What you're asking just can't be done - it's an ___impossibility.

在目前的预算限制下，按时完成这个项目是不可能的。

With the current budget constraints, finishing the project on time is an ___impossibility.

建造永动机被认为是理论上的不可能。

Building a perpetual motion machine is considered a theoretical ___impossibility.