While managing a large project, the project manager decided to include indirect costs as part of his cost estimate. If indirect costs are included in an estimate which of the following is true?

A. Indirect costs should be included at the activity level or higher levels.

B. Indirect costs must be included at the activity level only.

C. Indirect costs should only be included in earned value measurements and not in cost estimates.

D. Indirect costs should not be included in cost estimates.