Parents purchased a new mobile home from Seller. The mobile home was manufactured by Mobilco and had a ventilating system designed by Mobilco with both a heating unit and an air conditioner. Mobilco installed a furnace manufactured by Heatco and an air conditioning unit manufactured by Coolco. Each was controlled by an independent thermostat installed by Mobilco. Because of the manner in which Mobilco designed the ventilating system, the first time the ventilating system was operated by Parents, cold air was vented into Parents' bedroom to keep the temperature at 68Â°F (20Â°C). The cold air then activated the heater thermostat, and hot air was pumped into the bedroom of Child, the six-monthold child of Parents. The temperature in Child's room reached more than 170Â°F (77Â°C) before Child's mother became aware of the condition and shut the system off manually. As a result, Child suffered permanent physical injury. Claims have been asserted by Child, through a duly appointed guardian, against Mobilco, Seller, Heatco, and Coolco."If Child's claim against Seller is based on negligence, the minimum proof necessary to establish Seller's liability is that the ventilating system
was defective. was defective and had not been inspected by Seller. was defective and had been inspected by Seller, and the defect was not discovered.  was defective, and the defect would have been discovered if Seller had exercised reasonable care in inspecting the system