科学探索中仍有许多未知等待发现。

There are still many ___unknowns waiting to be discovered in scientific exploration.

在开始这个项目之前，我们需要考虑所有可能的未知因素。

Before starting this project, we need to account for all possible ___unknowns.

这个数学问题中有三个未知数需要计算。

There are three ___unknowns to calculate in this math problem.