终止心绞痛发作最有效、作用最快的药物是（）
A.受体阻滞剂
B.钙离子拮抗剂
C.阿司匹林
D.硝酸酯类药物
E.潘生丁
参考答案：D
阐述地质雷达接收单元的工作原理。
_______ he was rich, he gave little money to the others. [ ]
A. Because
B. Though
C. As
D. Since
