to suddenly understand
茅塞顿开
(máo sè dùn kāi)
A: I couldn't figure out the answer to this question for a while. But once you pointed it out, I suddenly understood. Thanks a lot.
这道题目,我本来想不出来。 听了你的话,我突然茅塞顿开。真的谢谢你。
(zhè dào tímù,wǒ běnlái xiǎnɡ bù chūlái, tīnɡle nǐ de huà,wǒ tūrán máo sè dùn kāi, zhēnde xièxiè nǐ.)
B: You're welcome.
不客气。
(bù kèqì.)