一般情况下，舒张压的高低主要反映（）
A．每搏输出量的多少
B．每分输出量的多少
C．外周阻力的大小
D．大动脉弹性的高低
参考答案：C
— Liu Fang, I didn't know you can play the Pipa and Guzheng so well.
— Well, actually I ________ it since I was six years old. [ ]
A. plays
B. have been playing
C. played
D. had been playing
在流行病学现场调查中，为组织方便和节约费用，选择哪一种抽样方法更合适（）
A.多级抽样
B.分层抽样
C.系统抽样
D.整群抽样
E.单纯随机抽样
