13. A variable overhead spending variance is caused by
    1. a. using more or fewer actual hours than the standard hours allowed for the production achieved.
    2. b. paying a higher/lower average actual overhead price per unit of the activity base than the standard price allowed per unit of the activity base.
    3. c. larger/smaller waste and shrinkage associated with the resources involved than expected.
    4. d. both b and c are causes.