Sentence:  It <WSD>is</WSD> indeed true , as stated in the famous novel of our day , `` For Whom the Bell Tolls '' , that `` no man is an island , entirely of itself ; every man is a piece of the continent , a part of the main '' . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)