请随手关门，外面风很大。

Qǐng suíshǒu guānmén, wàimiàn fēng hěn dà.

Please close the door behind you; it's very windy outside.

有人在门外敲门，你去看看是谁。

Yǒu rén zài mén wài qiāomén, nǐ qù kànkan shì shéi.

Someone is knocking at the door outside; go see who it is.

这扇门已经很旧了，该换一扇新的了。

Zhè shàn mén yǐjīng hěn jiù le, gāi huàn yī shàn xīn de le.

This door is already very old; it's time to replace it with a new one.