可待因是（）
A.半合成镇痛药物
B.合成镇痛药物
C.天然生物碱类镇痛药物
D.内原性多肽镇痛药物
E.非甾体抗炎镇痛药物
参考答案：A
北冰洋有哪些鲸鱼？
Yuan Longping is a scientist __________ is famous for the development of rice.[ ]
A. that
B. whom
C. what
D. which
