Detailed Answer
Answer (D) is correct.
Learning curves reflect the increased rate at which people perform tasks
as they gain experience. The time to perform a given task becomes
progressively shorter during the early stages of production. The curve is
expressed as a percentage reduction in time to complete a task for each
doubling of cumulative production. A learning curve percentage of 80%
is common. One model assumes that the cumulative average time per
unit for all production is reduced by a constant percentage. Another
assumes that the average time to produce the last unit is reduced by a
constant percentage.