Which of the following is an internal accounting control weakness related to factory equipment?

(a) Checks issued in payment of purchases of equipment are not signed by the controller.

(b) All purchases of factory equipment are required to be made by the department in need of the equipment.

(c) Factory equipment replacements are generally made when estimated useful lives, as indicated in depreciation schedules, have expired.

(d) Proceeds from sales of fully depreciated equipment are credited to other income.