我们住在大楼的第二十一层。

We live on the twenty-first floor of the building.

她住在这栋楼的第二十一层。

She lives on the twenty-first floor of the building.

他在比赛中获得了第二十一名。

He finished the race in twenty-first place.

这是我第二十一次来这家餐厅。

This is my twenty-first visit to this restaurant.

这本书的第二十一章是最精彩的。

The twenty-first chapter of the book is the most exciting.

这是她第二十一次尝试通过考试。

This is her twenty-first attempt to pass the exam.

今天是我弟弟的第二十一个生日。

Today is my brother's twenty-first birthday.

第二十一世纪见证了科技的快速进步。

The twenty-first century has seen rapid technological advancements.

她举办了一个盛大的派对来庆祝她的第二十一个生日。

She celebrated her twenty-first birthday with a big party.

祷告前的晚读，他选了《启示录》的第二十一章。

For the evening reading before prayers, he selected the twenty-first chapter of Revelation.