题目：
选择题
The best-known scientific achievement in the 19th century was ＿＿＿＿＿＿＿development of a theory of ＿＿＿.
- A. Francis Crick, molecular structure
- B. Charles Robert Darwin, evolution
- C. Paul Dirac,wave mechanics
- D. J.J. Thomas, new physics
答案：
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