Answer (D) is correct.
Mix and yield variances are the components of the usage (quantity or
efficiency) variance. Mix and yield variances can only be calculated
when inputs are substitutable. The yield variance measures how
efficiently the actual mix of inputs was used to produce the given output.
The yield variance equals standard total quantity (STQ) minus the actual
total quantity (ATQ) times the weighted-average standard price of the standard mix of inputs (SPSM).