Answer (C) is correct. The learning curve reflects the increased rate at which people perform tasks as they gain experience. The time required to perform a given task becomes progressively shorter. Ordinarily, the curve is expressed in a percentage of reduced time to complete a task for each doubling of cumulative production. One common assumption in a learning curve model is that the cumulative average time (and labor cost) per unit is reduced by a certain percentage each time production doubles. Thus, a 90% learning curve indicates that a doubling of production will reduce the cumulative average unit completion time by 10%. For example, if the first unit required 50 hours to complete, the average completion time e 45 hours (90% × 50 hours). If production is again doubled (to four units), the cumulative average completion time will be 40.5 hours (90% × 45 hours).