Hi Yuri, Imagine that Yuri sees a person. Yuri will use the word "you" to refer to that person. The room belongs to that person. So Yuri uses "your" to refer to someone's room. So, the final answer is "I (Yuri) am happy to see you (that person) cleaning your (that person's) room. I hope this helps. Cheers, Lance

"I am happy to see you cleaning your room" is correct.

C I'm happy to see you are cleaning your room.