A clear conscience is a soft pillow. 問心無愧，高枕無憂。

A clear conscience is a sure card. 光明磊落，勝券在握。

A clear conscience laughs at false accusations. 白日不做虧心事，夜半敲門心不驚。

A clear fast is better than a dirty breakfast. 寧為清貧，不為濁富。

A close mouth catches no flies. 病從口入，禍從口出。

A cock is valiant on his own dunghill. 夜郎自大。

A common danger causes common action. 同仇敵愾。

A constant guest is never welcome. 久住非佳賓，常來不歡迎。

A contented mind is perpetual feast. 知足常樂。

A covetous man is good to none but worse to himself. 貪婪的人對別人毫無好處，對自己卻壞處更大。

A crafty knave needs no broker. 狡猾的流氓，不需居間人。

A creaking door hangs long on its hinges. 戶樞不蠹。

Action is the proper fruit of knowledge. 行動是知識的巧果。

Actions speak louder than words. 事實勝于雄辯。

A discontented man knows not where to sit easy. 不滿足者坐無寧時。

A disease known is half cured. 病情確診斷，治病好一半。

Admonish your friends in private, praise them in public. 在私底下要忠告你的朋友，在公開場合又表揚你的朋友。