In twenty-first Century, the human has entered information age.

　　21世紀，人類(lèi)已經(jīng)完全進(jìn)入了信息化時(shí)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(gè)發(fā)展的時(shí)代、挑戰的時(shí)代、競爭的時(shí)代！

　　Some people have a big party for their twenty-first birthday.

　　一些人會(huì )在他們21歲生日舉行盛大的聚會(huì )。

　　In twenty-first Century, population aging is a global phenomenon.

　　21世紀的今天，人口老齡化已經(jīng)是全球化的現象了。