我wǒ们men生shēng活huó在zài二èr十shí一yī世shì纪jì。

We live in the twenty-first century.

这zhè座zuò桥qiáo已yǐ有yǒu半bàn个gè世shì纪jì了liǎo。

This bridge is already half a century old.

上shàng个gè世shì纪jì发fā生shēng了liǎo很hěn多duō变biàn化huà。

Many changes happened in the last century.

这zhè是shì本běn世shì纪jì最zuì重zhòng要yào的de发fā现xiàn。

This is the most important discovery of this century.

一yī个gè世shì纪jì有yǒu一yī百bǎi年nián。

A century has one hundred years.