In twenty-first Century, the human has entered information age.
21世紀，人類已經(jīng)完全進入了信息化時代。
Knowledge economy will play a leading role in the twenty-first century.
21世紀是知識經(jīng)濟占主導地位的世紀。
The twenty-first century is a time of development, challenges and competition.
二十一世紀是一個發(fā)展的時代、挑戰(zhàn)的時代、競爭的時代！
Some people have a big party for their twenty-first birthday.
一些人會在他們21歲生日舉行盛大的聚會。
In twenty-first Century, population aging is a global phenomenon.
21世紀的今天，人口老齡化已經(jīng)是全球化的現(xiàn)象了。