Which of the following elements is (are) needed in a straightforward calculation of the variable-overhead spending variance? Select one: a. Standard variable overhead applied to production. b. Variable overhead incurred during the period. c. Budgeted variable overhead based on actual hours worked. d. Both variable overhead incurred during the period and standard variable overhead applied to production. e. Both variable overhead incurred during the period and budgeted variable overhead based on actual hours worked.