The correct answer is: A. Unit of quantity of product, service or time in relation to which costs may be ascertained or expressed.
A cost unit is a unit of measurement used to assign costs to products, services, or activities. It can be a physical unit, such as a pound of product or a labor hour, or it can be a time period, such as a month or a year. The cost unit is used to calculate the cost per unit of output or the cost per unit of time.
Option B is incorrect because a cost center is a location, person, or item of equipment or a group of these for which costs are ascertained and used for cost control.
Option C is incorrect because a profit center is a centre having the responsibility of generating and maximising profits.
Option D is incorrect because a return on investment (ROI) center is a centre concerned with earning an adequate return on investment.