(someone had) Better keep quiet about it: 

(Someone had) better not say anything about a particular issue or situation. 

對某事保持沉默 √

例句：

Better keep quiet about it so that the boss doesn't suspect anything.

最好保持沉默，這樣老板就不會懷疑任何事情。

Keep one's head:

To remain calm and sensible when in an awkward situation that might cause a person to panic or go out of control. 

冷靜 √

例句：

She was very angry. We had to calm her down and encourage her to keep her head.

她非常生氣。我們必須使她平靜下來，并鼓勵她保持冷靜。

Keep on top (of someone or something)

To stay well-informed about the status of someone or something. 

駕馭；保持優(yōu)勢 √

例句：

You will get out of shape easily if you don't keep on top of things. 

徜若你不能掌控這些事情，很容易陷入不利的境地。

Song for you（片尾曲）

張含韻、藍心羽 - 丹青墨綠