缓解急性心肌梗死剧烈疼痛效果最好的是（）
A.硝酸甘油
B.二硝酸异山梨醇
C.罂粟碱
D.吗啡
E.可待因
参考答案：D
I ___________ some English books.[ ]
A. have
B. has
C. had
D. having
简便计算：1995+1996+1997+1998+1999+2000．
