Sentence:  One of those delightful surprise additions , which so frequently occur in jazz programs , <WSD>was</WSD> an excellent stint at the drums by the great Joe Jones , drumming to `` Old Man River '' , which seems to have been elected the favorite solo for the boys on the batterie at this year 's concerts . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)