The correct answer is $\boxed{\text{B) 25}}$.
The latest occurrence time for an event is the latest time that the event can occur without delaying the project. To calculate the latest occurrence time for event 2, we first need to calculate the earliest occurrence time for event 2. The earliest occurrence time for event 2 is the earliest time that all of the activities that must be completed before event 2 can be completed. In this case, the activities that must be completed before event 2 are activities A and B. The earliest occurrence time for activity A is 10, and the earliest occurrence time for activity B is 20. Therefore, the earliest occurrence time for event 2 is 20.
The latest occurrence time for event 2 is the contractual obligation time for the project minus the total float for event 2. The total float for event 2 is the amount of time that event 2 can be delayed without delaying the project. In this case, the total float for event 2 is 5. Therefore, the latest occurrence time for event 2 is 75 – 5 = $\boxed{\text{25}}$.
Here is a brief explanation of each option:
- Option A: 20. This is the earliest occurrence time for event 2. However, it is not the latest occurrence time because event 2 can be delayed by up to 5 days without delaying the project.
- Option B: 25. This is the correct answer. It is the latest occurrence time for event 2 because it is the contractual obligation time for the project minus the total float for event 2.
- Option C: 35. This is the latest occurrence time for event 2 if there is no total float for event 2. However, there is a total float of 5 days for event 2, so event 2 can be delayed by up to 5 days without delaying the project.
- Option D: 15. This is the earliest occurrence time for activity A. However, it is not the latest occurrence time for event 2 because event 2 can be delayed by up to 5 days without delaying the project.