I didn't know you were so busy.变被动语态
网友回答
That you were so busy was not known by me
======以下答案可供参考======
供参考答案1:
You weren't known to be so busy by me.
供参考答案2:
You weren't known to be so busy
供参考答案3:
It was not known to me that you were so busy.
供参考答案4:
That you were so busy was not known by me.