grammar

I've started making grammar flash cards based on the lessons of the Dangdai - A Course in Contemporary Chinese books commonly used in Taiwan. I've only covered book 1 of 6 so far for testing purposes and I'm looking for volunteers to help me test and adjust as needed. TL;DR These cards are...

Hello, I have met a sentence like: "他学的是中文" in one of the Chinese Breeze books. The meaning is mostly clear, but I couldn't find on internet the purpose of "的是". Does it mean a completed action? Could somebody explain why it's used and what is the difference between the sentence above and just...