Sentence:  The second agreement permits the authority to sell a 520 - acre tract west of Stage 1 Residential to Philadelphia Builders Eastwick Corp. , a firm composed of 10 Philadelphia area builders , which <WSD>is</WSD> interested in developing part of the project . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)