I think the talk given by the old scientist is worth .A. very, to listenB. well, listenin

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A. very, to listen
B. well, listening　
C. very, to listen to
(答案→)D. well, listening to
解析：考查worth的用法。be well worth doing sth.“很值得做某事”，well修饰worth。句意“我认为那位老科学家的演讲很值得一听。”故选D。