这份合同必须以书面形式确认。

Zhè fèn hétóng bìxū yǐ shūmiàn xíngshì quèrèn.

This contract must be confirmed in written form.

老师要求我们交一份书面报告，总结这次实验。

Lǎoshī yāoqiú wǒmen jiāo yí fèn shūmiàn bàogào, zǒngjié zhè cì shíyàn.

The teacher asked us to hand in a written report summarizing this experiment.

他的书面表达能力很好，但口语还需要提高。

Tā de shūmiàn biǎodá nénglì hěn hǎo, dàn kǒuyǔ hái xūyào tígāo.

His written expression is very good, but his speaking still needs improvement.