Fear is something that you are born with. You can't  ________ yourself of it completely but you

can ________ certain fears under certain conditions.[ ]

A. get; overcome  

B. rid; overcome

C. overcome; rid of  

D. break; get rid of

计算题：已知原水中阳离子量为4.5mmol/L，失效时钠离子量为0.3mmol/L，阳床直径为2.5m，树脂层高1.8m，制水量为1920t，求阳离子交换树脂的工作交换容量。