Sentence:  The cost of developing a major weapon system <WSD>is</WSD> now so enormous that the greatest care must be exercised in selecting new systems for development , in determining the most satisfactory rate of development , and in deciding the proper time at which either to place a system into production or to abandon it . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)