Final answer:
The requisition priority at the Source of Supply (SOS) is determined by the combination of the Force Activity Designator and Priority Designator codes.
Step-by-step explanation:
The combinations of codes that determine the requisition priority to be used at the Source of Supply (SOS) are Force Activity Designator and Priority Designator. These codes are part of a system used by military logistics to ensure that resources are allocated and prioritized according to the urgency of need and the importance of the mission or unit making the request. The Force Activity Designator indicates the relative importance of the unit or activity, while the Priority Designator reflects the urgency of the request based on operational considerations.