How should a developer configure the calculation procedure to conditionally execute the correct formula?

A developer need to configure a calculation procedure to calculation a subtotal using two different depending on whether the input Boolean variable is Customer is set to true or false.

How should a developer configure the calculation procedure to conditionally execute the correct formula?
A . Use two separate Calculation Steps with the Conditional Step property selected: use the ISTRUE(isCustomer) and NOT (ISTRUE) (isCustomer) functions in the Condition syntax.
B. Use two separate Calculation Steps with the Conditional Step property selected: reference just the isCustomer variable in the Conditional syntax (no comparison necessary)
C. Use two separate Calculation Steps with the Conditional Step property selected: compare the isCustomer variable directly to the literal true and false values in the Condition syntax.
D. Use a single Calculation Steps with IF statement directly in the formula definition to
reference the isCustome variable and conditionally perform the appropriate calculation.

Answer: B