我们没去游泳，原因很简单，水太冷了。

We didn't go swimming for the ___simple reason that the water was too cold.

我非常喜欢和动物一起工作，简单的原因是我计划成为一名兽医。

I'm very fond of working with animals, and the ___simple reason is that I'm planning to become a vet.

他拒绝了那个提议，原因很简单，它与他的价值观不符。

He refused the offer for the ___simple reason that it didn't align with his values.