The following diagram represents the behaviour of one element of cost: $ Total cost Volume of activity 0 Which ONE of the following statements is consistent with the above diagram? A Annual factory power cost where the electricity supplier sets a tariff based on a fixed charge plus a constant unit cost for consumption but subject to a maximum annual charge. B Weekly total labour cost when there is a fixed wage for a standard 40 hour week but overtime is paid at a premium rate. Total direct material cost for a period if the supplier charges a lower unit cost on all units once a certain quantity has been purchased in that period. D Total direct material cost for a period where the supplier charges a constant amount per unit for