嗯! 你怎么还没下班呢？

Ng! Nǐ zěnme hái méi xiàbān ne?

Huh! Why are you still not off work?

她正在认真思考，嗯了一声后继续沉默。

Tā zhèngzài rènzhēn sīkǎo, ōnle yī shēng hòu jìxù chénmò.

She was thinking seriously, and after a "hmm," she continued to remain silent.

他嗯了一声，表示同意了我的观点。

Tā ōnle yī shēng, biǎoshì tóngyìle wǒ de guāndiǎn.

He responded with a "hmm" to indicate his agreement with my viewpoint.