我信你。
wǒ xìn nǐ.
I believe you.
他不信我。
tā bù xìn wǒ.
He doesn't believe me.
我收到一封信。
wǒ shōu dào yì fēng xìn.
I received a letter.
他写了一封信。
tā xiě le yì fēng xìn.
He wrote a letter.
