Activity D on a CPM network has predecessors B and C$,$ and has successor F$.$ D has quration $6.$ 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 true?

Select the correct response:

All of the above are true

C is completec before B$.$

B is a critical activity

D is critical, and has zero slack

has no slack but is not critical.