one day i went out and left my key in the house. when i came back, i found i couldn't get in without my key. what should i do? after a moment, i got an idea. i picked up a big stone and was ready to break the window.

　　suddenly there came a deep voice, "what are you doing?" i turned over and saw a policeman was behind me. it took me quite a long time to explain myself. i won't be so careless again.