Please provide the correct answer for the below based on ahlei planning and control for food and beverage operations, ninth edition:

When constructing staffing guides, managers should: a. use the productivity rates of good employees as a basis to set labor standards for average employees. b. keep productivity rates at the levels initially established, despite increases in employee efficiency and proficiency. c. rely strongly on standards developed in the industry for other similar operations. d. incorporate all of the above points. answer : a correct?