The following SAS program is submitted:

  data WORK.TOTAL;

     set WORK.SALARY;

     by Department Gender;

     if First.<_insert_code_> then Payroll=0;

     Payroll+Wagerate;

     if Last.<_insert_code_>;

  run;

The SAS data set WORK.SALARY is currently ordered by Gender within Department.

Which inserted code will accumulate subtotals for each Gender within Department?

     A. Gender

     B. Department

     C. Gender Department

     D. Department Gender

Answer: A

First. and Last. 是什么意思？还有英语里 A within B 排序是AB还是BA？