B company, a text book manufacturer, incurred the following costs for the last 3 months:

Production in units:	40,000	50,000	60,000
Factory rent:	$10,000	$10,000	$10,000
Indirect Manufacturing costs:	$50,000	$60,000	$70,000
Selling costs:	$60,000	$75,000	$90,000
Commissions:	$120,000	$150,000	$180,000

Which of the following costs is variable?

Select one:

a. Both Commissions and Selling Costs

b. Commissions

c. Selling Costs

d. Factory Rent