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According to the activity network below, which one is not a critical activity? Activity C Activity F Activity G Activity B Consider the following activity network (where the time unit is an hour). If the activity time of B increases by 3 hours and the activity time of D increases by 2 hours, what is the change in project completion time? The project completion time increases by 2 hours. The project completion time keeps the same. The project completion time increases by 3 hours. The project completion time increases by 5 hours. What can we know from the following Gantt chart (assuming the time unit is an hour)? The slack time of activity C is 2 hours. There exists an unnecessary delay in the project. Activity D should be the predecessor activity of activity B. Activity A is not allowed to start at time 0