To Calculate the Probability of Completing a Project by a Certain

To calculate the probability of completing a project by a certain date,

A) the expected completion time of the project is taken to be the sum of the activity times on the shortest path.
B) the variance of the distribution of project completion times is taken to be one-sixth the difference between the latest finish time and the earliest finish time of the last activity in the project.
C) we assume that the activity durations are independent of each other so that the normal distribution can be used.
D) we only need the parameters of the beta distribution for the finish node of the diagram.