磁石、生石膏等药物的临床常用量是（）
A.3～9g
B.1.5～4.5g
C.9～45g
D.0.03～0.6g
E.0.3～1g
参考答案：C
John and I _____ friends for eight years. We first got to know each other at a Christmas party. But we ____ each other a couple of times before that.
A．had been; have seen
B．have been; have seen
C．had been; had seen
D．have been; had seen
磁感应强度相同的磁场中，长度相同的导线通以不同电流时，受力大小（）
A.相同
B.不同
C.无法确定
D.差别不大
