1. 他以前的尝试没有成功。

[ tā yǐ qián de cháng shì méi yǒu chéng gōng 。 ]

His previous attempts had been unsuccessful.

2. 巨大的努力确保了我们工作的成功。

[ jù dà de nǔ lì què bǎo le wǒ mén gōng zuò de chéng gōng 。 ]

Great efforts ensure the success of our work.

3. 只有努力，才能成功。

[ zhǐ yǒu nǔ lì ， cái néng chéng gōng 。 ]

Only by working hard can we succeed in doing everything.