conundrum|conundrums

这些数学难题让学生们感到非常困惑。

The math ___conundrums left the students completely puzzled.

老师给我们出了一个谜语：“什么东西越洗越脏？”

The teacher gave us a ___conundrum: "What gets dirtier the more you wash it?"

如何平衡工作和生活对许多人来说是个难题。

Finding a balance between work and life is a real ___conundrum for many people.