因為這里的不定冠詞是修飾名詞cottage，而不是修飾序數(shù)。又如：　　

The film is a costume drama based on a 19th-century novel. 這部電影是根據(jù)一本19世紀(jì)的小說拍成的古裝劇。　　

It is a 16th-century church with 18th-century embellishments. 那是一座有18世紀(jì)藝術(shù)裝飾的16世紀(jì)的教堂。　　

如果名詞中心詞前無需用冠詞，則此時修飾名詞的序數(shù)詞前也不能用冠詞。如：　　

The play is set in 15th-century Italy. 這出戲以十五世紀(jì)的意大利為背景。