Once I came back to my apartment after I finished my work.That day I was sick,so I wore a health mask.Before I opened the door of my room.I saw the door next my room with the key in the door knob. i thought the people in that room open the door and forget it.I have never know the owner that room ,but I decided knock on that door to inform and remind the owner that it should not be forgotten.i wait a while,a voice from inside that room rang.The tone was not friendly at all. I answered her that the door is still closed. Excuse me, I stay next you room i think you forget your key in the door knob. I said with a pronounce friendly. I hope she will not suspect and open the door. she was open the door and looked at me with my health mask.