病例对照研究选择病例时有那几种情况
A．新发病例
B．现患病例
C．死亡病例
D．医院病历
E．以上都是
参考答案：A,B,C
一When did you buy this still life picture?
一It was in 1999 I traveled in Paris．
A．since
B．that
C．when
D．before
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