Shouting to report it seems childish. Only by gently knocking on the door can you show that you are a college student. Just pay attention to the following points when knocking at the door:

(1) The most gentlemanly thing to do is to knock three times, and then knock a few times every once in a while. Don't knock too fast, and don't knock continuously with gravity. The volume should be moderate, so light that others can't hear it, so big that others resent it.

(2) When you knock on the door several times and no one answers, you should think that there may be no one in the office of the respondent, so don't knock again.

(3) If you knock on the wrong door, you should immediately apologize to the other party politely and say "I'm sorry". Don't turn away without saying a word.