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 tasks are on critical path?