Which of the following equation is NOT valid regarding spending variances shown in the flexible budget performance report? A. Total spending variance for direct labor = labor rate variance + labor efficiency variance. B. Total spending variance for variable overhead = variable overhead rate variance + variable overhead efficiency variance. C. Total spending variance for direct materials = material price variance + material quantity variance, if actual quantity purchased = actual quantity used. D. Total spending variance for fixed overhead = fixed overhead budget variance + fixed overhead volume variance.