你在中国学习的时候，碰到过什么问题吗？

Nǐ zài Zhōngguó xuéxí de shíhou, pèngdào guò shénme wèntí ma?

When you studied in China, did you run into any problems?

他在工作中碰到问题，就会问同事。

Tā zài gōngzuò zhōng pèngdào wèntí, jiù huì wèn tóngshì.

When he runs into problems at work, he asks his colleagues.

我没想到会在这里碰到你。

Wǒ méi xiǎngdào huì zài zhèli pèngdào nǐ.

I didn't expect to run into you here.