Sentence:  These factors practically insure that no single financing formula <WSD>is</WSD> feasible ; each situation must be studied and a plan developed that takes into consideration such factors as the effect of the existing and prospective tax calendars , the financial condition of the treasuries , and the length of the transition interval . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)