由因到果的研究属于（）
A.诊断试验
B.队列研究
C.筛检
D.病例对照研究
E.现况研究
参考答案：B
He didn't agree with me at first but I _______ persuade him. [ ]
A. was able to
B. could
C. could be able
D. should
祥瑞一生是典型的终身寿险。（）
