A project has six tasks which are required for completion: Tasks A, B, C, D, E and F. The relationship between the tasks is described below: Task A takes 8 weeks. Task B takes 3 weeks. Task A must be completed before beginning Task C. Task C takes 7 weeks. Both Tasks A and B must be completed before beginning Task D. Task D takes 3 weeks. Task E takes 4 weeks. In order to begin Task E, Task C must first be completed. Task F takes 6 weeks. In order to begin Task F, Task D must first be completed. Which of the following is the correct Slack Time for Task D?

a. 2

b.1

c.3

d. it cannot be determined