-This is the music.
-How do you know?
-Is it Morse code?
-Maybe the password? 

——Les Choristes

-这是乐谱。
-你怎么知道?
-是摩斯码吗?
-也许是密码?

——《放牛班的春天》

一、关于password，你应该知道的用法有

n.

密码，口令 a secret word or phrase that you need to know in order to be allowed into a place

No one shall be allowed in unless he can give the password.

凡对不上口令的人将一律不准入内。

二、接下来，做个填词游戏吧

The _____ should be invisible.

密码应该是不可见的。