Sentence:  For this period , as for earlier centuries , pottery remains the most secure source ; the ceramic material of the age <WSD>is</WSD> more abundant , more diversified , and more indicative of the hopes and fears of its makers , who begin to show scenes of human life and death . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)