Final answer:
MRCs are issued by organizations responsible for the maintenance and contain scheduled maintenance requirements applicable to O-level and I-level activities for specific aircraft or equipment.
Step-by-step explanation:
The subject of this question is engineering. Specifically, it is related to maintenance requirements for aircraft or equipment. MRCs (Maintenance Requirements Cards) are issued by the organization responsible for the maintenance of the aircraft or equipment, such as the manufacturer or the military. These cards contain scheduled maintenance requirements applicable to different levels of activities, such as O-level (Organizational-level) and I-level (Intermediate-level) activities.