Sentence:  Certainly , in analyzing an action which truly faced such alternatives , `` it <WSD>is</WSD> never possible that no world would be preferable to some worlds , and there are in truth no circumstances in which the destruction of human life presents itself as a reasonable alternative '' . 
Meaning of the word marked with <WSD> tags:  have the quality of being; (copula, used with an adjective or a predicate noun)