A car servicing station is running a special offer. The breakdown of the cost for different services is given below. Membership Fee: $50 (one-time cost) Air Freshener Cost: $4 per car per month Washing Cost: $10 per car per month Tire Replacement Cost: $400 per car Tire Pressure Check Cost: $15 per month The total cost for 12 months of this service for n cars is given by the expression below. Which statement best describes the constant in the expression? A. It is the monthly cost of the air freshener, washing, and tire replacement. B. It is the monthly cost of the membership fee and the tire pressure check. C. It is the total cost of the membership fee and the tire pressure check for 12 months. D. It is the total cost of the air freshener, washing, and tire replacement for 12 months.