Select the option that describes roll$-$up estimating.

a$.)$

This includes only the true costs for completing a project, without providing any options for changes.

b$.)$

This involves estimating project costs by specifying a value for the smallest details of each project activity.

c$.)$

This identifies money that should be added to a project budget to manage potential project overages.

d$.)$

This refers to budgets from previous projects that are similar to create estimates for the current project.