can you help with answer for below, i believe (b) is correct answer, any views?

During planning processes, you used Monte Carlo simulation to quantitatively assess cost and schedule risks of your project. During risk control, you repeat the technique, and it leads to different results. What should not be the reason for that?

o Some assumptions during planning have meanwhile become fact-based knowledge, so that the risks related to them have vanished or have become certain problems.
o New risks may have been identified. These influence the input data used for Monte Carlo simulation in a way which was not predictable at the time when the simulation was run.
o Some constraints have been identified originally, but their influence on the project was unclear when the simulation was run for the first time. By now, the team understands these constraints much better and has been able to adjust the simulation.
o Some dummy activities in the network logic have an element of uncertainty, which gets bigger over time. While the project proceeds, it gets even harder to predict how the team members assigned to them will perform.