理由: reason

遅おくれた理由りゆうを教おしえてください。

Please tell me the reason you were late.

気候きこうが寒さむくなって、食べ物たべものが減へったことが、理由りゆうの一ひとつだといわれます。

It is said that one reason was that the climate got colder and food became scarcer.