【错误表达】

It is important that you must study hard.

你要努力学习，这很重要。

【讲解辨析】

主句中有important这个形容词，后面的主语从句要使用虚拟语气，谓语结构为should+动词原形。其中should可以省略。

【正确表达】

It is important that you should study hard.

It is important that you study hard.

【举一反三】

It is important that we should keep the balance of nature.

It is important that we keep the balance of nature.