Sentence:  The construction was reasonably solid ; not like the cracker-box construction of so many of the motel units that have stucco all over the outside but walls that <WSD>are</WSD> thin enough so you can hear every movement of the people in the adjoining apartment . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)