The correct answer is: D. On original critical activities and those that become critical at any stage of crashing in the order of ascending cost slope.
Crashing is a technique used in project management to shorten the project schedule by adding resources to activities. This can be done by adding more people, equipment, or working overtime. However, crashing usually comes at a cost, as it can increase the cost of the project.
The goal of time-cost optimization is to find the best combination of time and cost for the project. This can be done by crashing the critical activities first, and then crashing the non-critical activities that become critical as a result of crashing the critical activities. The activities should be crashed in the order of ascending cost slope, which means that the activities with the highest cost per unit of time should be crashed first.
Here is a brief explanation of each option:
- Option A: Crashing is not done on all the activities. In fact, crashing should only be done on the critical activities, as these are the activities that have the most impact on the project schedule.
- Option B: Crashing is not done on all the activities lying on the critical path. In fact, some activities on the critical path may not be worth crashing, as the cost of crashing them may be more than the benefit of shortening the project schedule.
- Option C: Crashing is not only done on activities lying on the original critical path and having flatter cost slopes. In fact, activities that become critical at any stage of crashing should also be crashed, regardless of their cost slope.
- Option D: This is the correct answer. Crashing is done on original critical activities and those that become critical at any stage of crashing in the order of ascending cost slope.