【专八改错题.冠词.1.Withoccasionalbreaksforwar,theratesofdeathandinfectionintheEuropeandAmericadroppedsteadilythroughthe19thand20thcenturies.这题错误的是Europe前面的the要去掉.那为什么19th前面的the不用】

　　专八改错题.冠词.

　　1.Withoccasionalbreaksforwar,theratesofdeathandinfectionintheEuropeandAmericadroppedsteadilythroughthe19thand20thcenturies.

　　这题错误的是Europe前面的the要去掉.那为什么19th前面的the不用去掉呢?19世纪不是也只有一个吗?

　　2.Thereisrelativelylittledivisionoflaborintospecializedduties.Rather,eachpersonisexpectedtoperformgreatvarietyoftasks,thoughdutiesmaydifferbetweenthesexes.

　　为什么sexes前面要加the?