Our Account Receivable Department has written to you three times

Our Account Receivable Department has written to you three times; _________, you have given no response to our letter.
A、but
B、however
C、therefore
D、moreover
【正确答案】：B
【题目解析】：句意：我们的应收账款部门已经给您写过三次信：然而，你却没有给我们回信。but意为”但是“，其后一般不用逗号；however意为“然而”，其后经常用逗号；therefore意为“因此”；moreover意为“而且”。