前天和昨天都下雨了。

Qiántiān hé zuótiān dōu xiàyǔ le.

It rained both the day before yesterday and yesterday.

前天我去北京了。

Qiántiān wǒ qù Běijīng le.

The day before yesterday I went to Beijing.

我前天买了这本书。

Wǒ qiántiān mǎi le zhè běn shū.

I bought this book the day before yesterday.