Final answer:
The project manager likely instructed that the activities not scheduled to start should either be set to 0% completeness or not included in the Risk Index calculations, represented by option D) A or C.
Step-by-step explanation:
When a project team is performing a Project Risk Assessment and encounters project activities that have not been scheduled to start, there are a couple of plausible ways to handle these in the assessment. The project manager resolved the issue by suggesting the correct approach. In this scenario, the most accurate answer would be that the completeness for these activities is set to 0% as they have not started, or they are not included in the calculation of the Risk Index. Therefore, the best answer would be option D) A or C.