Sentence:  Although the tape was run for over 1 hr. , a steady state was not reached , and it was concluded that the reason for this was that the back pressure of the manometer was built up from the material fed from between the blocks and this <WSD>was</WSD> available at a very slow rate . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)