他们在演奏二十世纪的古典音乐。

Tāmen zài yǎnzòu èrshí shìjì de gǔdiǎn yīnyuè.

They are playing classical music of the 20th century.

我最近在研究二十世纪我国的历史。

Wǒ zuìjìn zài yánjiū èrshí shìjì wǒguó de lìshǐ.

Recently I've been researching the history of my country in the 20th century.

上个世纪，这个城市还是一个小村子。

Shàng gè shìjì, zhège chéngshì háishi yí gè xiǎo cūnzi.

In the last century, this city was still a small village.