C: · My pen name is "Hai Ying".

C：·我的笔名叫海燕。

I: What's your pen name?

I：你的笔名叫什么？

Yes, my pen name is Bai Yun.

有，我的笔名叫白云。

Do you have a pen name?

你有笔名吗？

Mark Twain is his pen name.

马克·吐温是他的笔名。