Sentence:  Today , according to land economist Homer Hoyt , shopping centers and their associated parking lots cover some 46000 acres of land , which is almost exactly the total land area in <WSD>all</WSD> the nation 's Central Business Districts put together . 
Meaning of the word marked with <WSD> tags:  quantifier; used with either mass or count nouns to indicate the whole number or amount of or every one of a class