Sentence:  The most distal airways are similar to those found in type 1 , , <WSD>being</WSD> composed of numerous , apparently true terminal bronchioles and occasional , poorly developed respiratory bronchioles ( figs. 14 , 15 ) . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)