题目

Lin Dan, the two-time defending world champion, raced to a 7-0 lead in the second game, _______ a stunned Lee Chong Wei started to even find his rhythm. A. before              B. after          C. since              D. once   答案：A  某学生进行小麦发芽试验共用了250粒种子，其中没有发芽的种子有10粒，发芽率是A.9％ B.95％ C.96％ D.98％