问题补充：
Scientists think they have in their attempt to find the causes of some major dieases.
A. broken through
B. worked out
C. fallen out
D. got round
答案：
(答案→)A. broken through
B. worked out
C. fallen out
D. got round
解析：本题译文：科学家认为他们在探索某些重要疾病的病因中已取得重大突破。break through(=be successful after overcoming a difficulty)突破；取得重大成果：Scientists hope to break through soon in their fight against heart disease.(科学家希望在与心脏病斗争中很快取得重大成果。)
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