Sentence:  In theory , compulsive behavior is a way of diminishing anxiety , and one might expect a negative association except for the possibility that for many children the obsessive-compulsive defenses <WSD>are</WSD> not sufficient to quell the amount of anxiety they suffer . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)