The eighteenth century developed a completely new kind of novel.

　　18世紀發展了一種全新的小說。

　　We got engaged on my eighteenth birthday

　　在我18歲生日那天我們訂婚了。

　　The siege is now in its eighteenth day.

　　圍困今天已經進入第18天了。

　　Such disputes multiplied in the eighteenth and nineteenth centuries

　　這類糾紛在18和19世紀大量增多。

　　The problem was not solved completely until the invention of the marine chronometer in the eighteenth century.

　　這個問題之道十八世紀發明了航海經線儀才得以解決。