Sentence:  What is noteworthy about this large group of teen-agers <WSD>is</WSD> that , although their attitudes hardly differentiate them from their gentile counterparts , they actually lead their lives in a vast self enclosed Jewish cosmos with relatively little contact with the non Jewish world . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)