他对我发火，原因我真是莫名其妙。

Tā duì wǒ fā huǒ, yuányīn wǒ zhēn shì mòmíngqímiào.

He got angry with me, and the reason was truly inexplicable.

这个问题的答案对我来说真是莫名其妙。

Zhège wèntí de dá'àn duì wǒ lái shuō zhēn shì mòmíngqímiào.

The answer to this question is truly inexplicable to me.

他脸上的表情让我感到十分莫名其妙。

Tā liǎn shàng de biǎoqíng ràng wǒ gǎndào shífēn mòmíngqímiào.

The expression on his face made me feel extremely inexplicable.