Last Month at Emil's Italian Restaurant, Actual Food Costs Fell

Last month at Emil's Italian Restaurant, actual food costs fell below standard food costs. Which of the following could be the reason?

A) failure to collect all revenue due
B) food production staff substituting lower quality ingredients than called for by standard recipes
C) larger portion sizes prepared by food production staff
D) higher prices charged by suppliers during the month that weren't reflected in the selling prices of affected menu items