我选择他的最大原因是因为他很善良。

Wǒ xuǎnzé tā de zuì dà yuányīn shì yīnwèi tā hěn shànliáng.

The biggest reason I chose him is because he is very kind.

你知道他放弃的原因是什么吗？

Nǐ zhīdào tā fàngqì de yuányīn shì shénme ma?

Do you know what caused him to give up?

你迟到的原因是什么？

Nǐ chídào de yuányīn shì shénme?

What is the reason you were late?