Sentence:  Those modern scholars who urge that we must keep in mind the fundamental continuity of Aegean development from earliest times - granted occasional irruptions of peoples and ideas from outside - <WSD>are</WSD> correct ; but all too many observers have been misled by this fact into minimizing the degree of change which took place in the early first millennium . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)