【题目】Scientists have made a major ________ in the treatment of cancer.
A. barrier B. breakthrough
C. companion D. concern
【答案】B
【解析】
考查名词词义辨析。句意：科学家在癌症治疗方面取得了重大突破。A. barrier障碍物；B. breakthrough突破；C. companion 同伴；D. concern关心。短语make a breakthrough突破。故选B。
