The correct answer is C.
The Rowan scheme is a piece-rate incentive plan in which workers are paid a base rate plus a bonus for production in excess of a standard. The bonus is calculated as a proportion of the time saved, or the difference between the standard time and the actual time taken to complete the job.
Option A is incorrect because the bonus is not paid as a proportion of standard time to actual time. The bonus is paid as a proportion of time saved to standard time.
Option B is incorrect because the bonus is not paid as a proportion of actual time to standard time. The bonus is paid as a proportion of time saved to standard time.
Option D is incorrect because the bonus is not paid as a proportion of standard time to time saved. The bonus is paid as a proportion of time saved to standard time.