Sentence:  When they reached their neighbor 's house , Pamela said a few polite words to Grace and kissed Melissa lightly on the forehead , the impulse prompted by a stray thought - of the type to which she <WSD>was</WSD> frequently subject these days - that they might never see one another again . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)