Complex projects such as research and development for new products often employ rolling wave planning to estimate costs. Which of the following best describes "rolling wave" planning?

a$.$ Project managers render a definitive estimate for the first stage and an order of magnitude estimate for the remainder of the project.

b$.$ Project managers render an order of magnitude estimate for the first stage and a definitive estimate for the remainder of the project.

c$.$ Project managers render definitive estimates for all stages of the project during initiation.

d$.$ Project managers render an order of magnitude estimate for all stages of the project.