Over years scientists have made a great in the treatment of cancer.A. break-inB. breakthr

问题补充：

Over years, scientists have made a great in the treatment of cancer.

A. break-in

B. breakthrough

C. breakup

D. breakdown

答案：

A. break-in

(答案→)B. breakthrough

C. breakup

D. breakdown

解析：词义辨析。 A. 闯入 B.突破 C. 解体 D. 故障；崩溃。句意：过去几年中我们在癌症的治疗方面取得了巨大的突破。故选B。