Activity $C$ on a CPM network has predecessor $B,$ and has successors $D$ and $F.$ C has duration $7$ days. B$\text{'}$s earliest finish is $20.$ D$\text{'}$s late start is $30,$ while F$\text{'}$s is $27.$ Which of the following is definitely TRUE?

D has no slack and is critical..

$B$ has slack and is not critical.

C is completed before $B.$

C has no slack and is critical.

F has slack and is not critical.