Which of the following is TRUE concerning operating income calculated under variable costing as compared to absorption costing? Select one: a. The relationship between production and sales has no bearing on the differences in operating income between the two methods. b. Operating income is higher under variable costing when production exceeds sales. c. Operating income is higher under variable costing when production exceeds sales only if there is a production-volume variance. d. Operating income is lower under variable costing when sales exceeds production only if there is a production-volume variance. e. Operating income is lower under variable costing when production exceeds sales