Answer: C - Critical path activities must be completed on time for the plan to be finished on schedule, and activities not on the critical path can be delayed for a time if resources need to be reallocated for any reason.
Key takeaway: The critical path defines those activities which are dependant on each other and which have the longest time span (for example, the longest chain of linked dependencies constitutes the critical path). Any delays on this path affect the entire schedule, whereas anything not on that path can be allowed some flexibility with the timeframe.