Activity D on a CPM network has predecessors B and C$,$ and has successor F$.$ D has duration $5.$ B$\text{'}$s earliest finish is $18,$ while C$\text{'}$s is $15.$ F$\text{'}$s late start is $23.$ Which of the following is definitely TRUE?

Group of answer choices:

B has no slack, and is critical.

F is not critical, and has slack.

C must be started after B is finished.

D is critical, and has a slack of five days.

C has no slack, and is critical.