原始凭证按照经济业务的类别不同，分为款项收付业务凭证、出入库业务凭证、成本费用凭证、购销业务凭证、固定资产业务凭证和转账业务凭证。
参考答案：对
—Can you give me some advice on what I said just now?
—Sorry, my mind ________.[ ]
A. has wondered
B. had wondered
C. is wondering
D. was wondering
成组资料比值比的分母为：（）。
A．暴露组某病某年发病率
B．暴露组某病某日患病率
C．病例组中暴露者数与对照组中非暴露者数的乘积
D．病例组中非暴露者数与对照组中暴露者数的乘积
