Which scenario would likely result in a High Risk situation?

Please select from one of the following:

a) Contract is experiencing minor overruns and contract schedule slip that will not result in the critical path

b) Likely that a shortage in parts will adversely affect the Contractor's ability to pass the Preliminary Design Review (PDR), a major milestone for next month

c) Contract is underrunning forecast spend plan

d) Contract schedule slip will not result in an impact to the critical path