81. What should the blank line below read to be able to output the sum of Qtr_total by the variable paid_by?

proc sort data=ecsql1.employee_donations out=work.employee_donations_sort;
by paid_by;
run;

data work.donations (keep=paid_by Qtr_total);
set work.employee_donations_sort;
by paid_by;
Qtr_total + Qtr1;
if _____________;
run;

a) last paid_by
b) paid_by.last
c) paid_by.last = 1
d) last.paid_by = 1

Answer: D