Sentence:  It <WSD>is</WSD> difficult to say what can be done about them except that we must learn to recognize when it is they , rather than pretexts for them , that are causing the trouble , and do everything possible to nurture the healthy personalities that will prevent the development of such deficiencies . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)