Answer (C) is correct. Learning curve models reflect the increased rate at which people perform tasks as they gain experience. One common assumption is that the cumulative average time per unit is reduced by a certain percentage when production doubles during the early stages of production. An 80% learning curve indicates that a doubling of production reduces the time required by 20%. For example, if the first unit requires 50 hours, the cumulative average completion time is 40 hours (80% × 50 hours) for two units and 32 hours (80% × 40 hours) for four units.