0 21st written as a word -- 第21，第二十一
the twenty-first century 二十一世纪
1 the day on which a person reaches the age of 21 and is traditionally said, in Western societies, to become an adult -- 21岁生日（西方的成人年龄）
Yet, almost paradoxically, four years into the twenty-first century, this book could hardly be timelier.
In the twenty-first century, the study of popular music can no longer be excluded from medieval music study.
Creating culturally relevant ways of thinking about diversity and aging : theoretical challenges for the twenty-first century.
Ultimately the genre survives in the twenty-first century primarily in our university choruses and local choral societies.
This is laudable but is not, in itself, enough to build or sustain a progressive coalition for the twenty-first century.
One must translate the symbolic imagery of these testimonies into a form useful to twenty-first-century historians.
But perhaps the heuristic capability of this novel lies in its ability to reconstruct coherences no longer apparent in the twenty-first century.
The twenty-first centur y, we are told, is going to be a centur y of cities.
