✅ The verified answer to this question is available below. Our community-reviewed solutions help you understand the material better.
You are designing a PERT graph for a Polaris missile subsystem. Activity B and Activity C can be executed simultaneously, but both can only start after Activity A is fully completed. Furthermore, Activity D cannot begin until both Activity B and Activity C are finished. If you draw this network exactly as described, what structural element is strictly mandatory to include between the events marking the completion of B and C, and why?