10. A pipeline 6000 meters long is to convey a sewage having some corrosive effect. Bids have been received for reinforced concrete, cast iron, and steel. Because of the varying hydraulic qualities of the inside surface of the reinforced concrete was to be 36 inches in diameter, the cast iron pipe 42 inches in diameter, and steel 45 inches in diameter. The assumed lengths of life of the materials are 100, 75, and 50 years for cast iron, concrete, and steel, respectively. Annual maintenance cost are assumed as P600 for cast iron, P900 for concrete, and P3,600 for steel. The bids are P770,000 for reinforced concrete, P790,000 for cast iron, and P580,000 for steel. Regarding the annual costs of the three, which of the following are true if money is worth 5%? A. steel pipe has the smallest annual cost B. cast iron pipe has the largest annual cost C. reinforced concrete pipe has the smallest annual cost D. steel pipe and cast iron pipe have the same annual cost