问题补充：
单选题Scientiststhinktheyhave_____intheirattempttofindthecausesofsomemajordieases.A.broken throughB.worked outC.fallen outD.got round
答案：
A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。)
