Sentence:  Thoroughly modern in treatment , they <WSD>are</WSD> at the same time , full of simple sincerity which invariably characterizes genuine Negro folk-music and are by no means to be confused with the average ' Broadway Spirituals ' which depend for their racial flavor upon sundry allusions to the ' Amen Corner ' , ' judgement day ' , ' Gabriel 's horn ' , and a frustrated devil - with a few random ' Hallelujahs ' thrown in for good measure . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)