他太沮丧了，无法保持理性。

He was too upset to be ___rational.

教授对这个现象给出了理性的解释。

The professor gave a ___rational explanation for the phenomenon.

尽可能保持理性，你就能第一次通过驾驶考试。

Be as ___rational as you can and you will pass your driving test the first time.