In the Critical Path Method (CPM) scheduling, the critical path is the longest sequence of dependent activities that determines the project duration.
Site work typically involves grading, excavation, underground utilities, and foundation preparation.
Site work must proceed in a linear, sequential manner: earthwork must finish before foundation pours; utilities are installed before slabs.
These activities are dependent on each other and cannot be done in parallel or out of order.
Therefore, site work forms a continuous chain of dependent activities on the critical path.
Other options are less relevant to CPM critical path logic:
Site work costs or retainage do not influence CPM scheduling.
Short interval scheduling is a project control technique, not a CPM determinant.
Reference:
NCARB ARE 5.0 Review Manual, Project Management and Scheduling chapter
CPM scheduling principles from project management texts like PMBOK or Construction Planning and Scheduling by Jimmie Hinze