The Following Questions Adapted from Tutorial Material of H Steyn

The Following Questions adapted from tutorial material of H Steyn Ed., Project Management -A Multi-disciplinary Approach (Pretoria: FPM Publishing, 2003). Reprinted with permission.
-Consider the schedule below:
RB = Resource Buffer
FB = Feeding Buffer
PB = Project Buffer
The letters A, B, C, D and E represent the resources needed to do the indicated activities.

(a) Show the critical chain on the sketch above.
(b) Why is there no resource buffer (RB) before the activity to be performed by A?
(c) Why is there no resource buffer before the second task to be performed by resource B?
(d) Would the 6-day duration shown for the activity to be performed by A be a pessimistic or a realistic value?