为评价某种药物预防冠心病的效果，最合适的研究方法是
A．横断面研究
B．病例对照研究
C．生态学研究
D．临床试验
E．队列研究
参考答案：D
乌头汤中有而桂枝芍药知母汤中没有的药物是（）。
A.黄芪
B.白蜜
C.川乌
D.细辛
E.草乌
Mr. Johnson's funny story _______ by everyone who heard it.
But Mr. Johnson himself didn't mind it at all. [ ]
A. laughed at
B. was laughed
C. had been laughed
D. was laughed at
