All things are difficult before they are easy.

　　凡事都是先难后易。

　　

　　Diligence is the mother of success.

　　勤奋是成功之母。

　　

　　Discontent is the first step in progress.

　　不满足是进步的开始。

　　

　　One false step will make a great difference.

　　失之毫厘，差以千里。

　　

　　Give him the dose of his own medicine.

　　以其人之道还治其人之身。

　　

　　Doube is the key of knowledge.

　　怀疑是知识的钥匙。