you didn`t hear my knocking at the door; you______ soundly w

you didn`t hear my knocking at the door; you______ soundly when i came in
答案是must be sleeping 是否应是must have been sleeping

答案是对的.
若用must have been sleeping则表示从过去某个时间点一直睡到现在；
而依题意应该仅是‘我’在敲门时,你睡得很香甜.
FYI:
现在完成进行时表示从过去某时开始一直持续到现在的动作,并且还将持续下去.
The Chinese have been making paper for two thousand years.
中国有2000年的造纸历史.（动作还将继续下去）
I have been learning English since three years ago.
自从三年前以来我一直在学英语.（动作还将继续下去）