obvious

students
这也太简单了吧。改成一句话好不好？
Students  are  singing  and  dancing.(若语法有错，请指点)

Good idea!

Any person shall struggle for his goal.

Lemon is a kind of fruit.

The wise man knows he knows nothing, the fool thinks he knows all.
清者自清，浊者自浊。

Lost time is never found again.
岁月既往，一去不回。

No way is impossible to courage.
勇者无惧。

Experience is the father of wisdom and memory the mother.
经验是智慧之父，记忆是智慧之母。

Rome is not built in a day.
冰冻三尺，非一日之寒。