The correct answer is: b) a debit to work in process.
When assigning factory overhead costs to specific jobs, a company records these costs as an increase to the Work in Process (WIP) account. This is because these overhead costs are considered a part of the total cost of producing goods. So, the entry to apply factory overhead involves debiting the Work in Process account, which reflects the accumulation of costs that are necessary to complete the manufacturing of a product. This allocation helps ensure that each job bears its fair share of production costs, including indirect costs like utilities, maintenance, and depreciation.