Nán ɡuài!
难怪!
No wonder!
Notes:
难(nán): be difficult
怪(ɡuài): feel strange
Example:
A:他英语真好。
Tā Yīnɡyǔ zhēn hǎo.
His English is really good.
B:他爸爸是英国人。
Tā bàbɑ shì Yīnɡɡuórén.
His father is from England.
A:难怪。
Nán ɡuài!
No wonder!