21的英文怎么寫序數(shù)詞

　　The battle would start the next morning — Sunday, July twenty-first.

　　這場戰(zhàn)役就要在第二天早晨，即7月21日星期日打響。

　　But in the twenty-first century, a very different story is unfolding.

　　但在21世紀(jì)，呈現(xiàn)在大家面前的又是另外一種故事。

　　I have no doubt that America can compete-and succeed-in the twenty-first century.

　　毋庸置疑，我認(rèn)為美國有實力參與21世紀(jì)的競爭并取得成功。