【题目】Over years，scientists have made a great________in the treatment of cancer.
A.breakin
B.breakthrough
C.breakup
D.breakdown

【答案】B
【解析】考查单词意思辨析。A项“非法进入，闯入”；B项“突破”；C项“破裂”；D项“失败，损坏”。根据句意“在过 去的几年里，科学家在癌症的治疗上已经取得了重大突破”。所以答案是B。