The correct answer is: C. May be longest or shortest.
The critical path is the longest path through a project network diagram. It determines the earliest possible completion time for the project. The critical path may be longest or shortest, depending on the specific project network diagram.
Option A is incorrect because the critical path is not always the longest path. For example, if there is a path through a project network diagram that has more tasks than the critical path, but the tasks on the longer path have shorter durations, then the longer path will be the critical path.
Option B is incorrect because the critical path is not always the shortest path. For example, if there is a path through a project network diagram that has fewer tasks than the critical path, but the tasks on the shorter path have longer durations, then the shorter path will be the critical path.
Option C is correct because the critical path may be longest or shortest, depending on the specific project network diagram.
Option D is incorrect because the critical path is not always the longest or shortest path.