Scientists have achieved a major in the search for a cure for cancer, is good news for t

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A. breakthrough; what
B. breakdown; which
C. breakup; that
(答案→)D. breakthrough; which
解析：考查名词和非限制性定语从句：句意：科学家在癌症疗法上已经有了重大发现，这对于癌症患者是好消息。第一空填A. 或D“breakthrough”突破，B. breakdown;破裂，C. breakup分手，第二空是非限制性定语从句，用which指代前面的句子，选D。