吸收过程的推动力是（）
A、气相浓度与液相浓度之差
B、实际浓度与平衡浓度之差
C、塔顶与塔底出口浓度之差
D、流体与界面上的浓度之差
参考答案：B
P代表该波对于规定的参考电极值为正向，N0 代表正常潜伏期在20ms左右的正向波。
Kim bought a total of $2.65 worth of postage stamps in four denominations. If she bought an equal number of 5-cent and 25-cent stamps and twice as many 10-cent stamps as 5-cent stamps, what is the least number of 1-cent stamps she could have bought ？（）
A.5
B.10
C.15
D.20
E.25
