Sentence:  This problem of fair and equitable assessment of value is a difficult one to solve in that the determination of fair valuation <WSD>is</WSD> dependent on local assessors , who in general are non-professional and part-time personnel taking an individualistic approach to the problem . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)