Activity D on a CPM network has predecessors B and$$ C$,$ and has successor F$.$ D has duration $6.$ B$\text{'}$s earliest finish is$18,$ while$$ C$\text{'}$s is $20.$ F$\text{'}$s late start is $26.$ Which of the following is definitely$$ true?

Part $2$

A$.$

D is$$ critical, and has a slack of two days.

B$.$

F is$$ critical, and has zero slack.

C$.$

C is completed before B$.$

D$.$

D has no slack but is not critical.

E$.$

B is a critical activity.