Structurally, this type of question is identical to a statement. In speech, the sentence ends with a raised pitch. In writing, the sentence ends with a question mark. This type of question is used either to indicate doubt or to convey mild surprise.
儿子:妈,我功课写完了,我要跟朋友出去玩。
ér zǐ :mā ,wǒ xiǎng gēn péng yǒu qù yóu yǒng ,háng bú háng ?
Son: Mother, I have finished my homework; I want to go out with my friends.
妈妈:你功课写完了?你才写了十分钟,就写完了?
mā mā :nǐ gōng kè xiě wán le ?nǐ cái xiě le shí fèn zhōng ,jiù xiě wán le ?
Mother: You have fi nished your homework? You only spent ten minutes writing. (= doing your homework) and you already finished?
[1] Yip, P. C., Rimmington, D., Xiaoming, Z., & Henson, R. (2009). Basic Chinese: a grammar and workbook. Taylor & Francis.