Final answer:
In a terminal digit filing system, the primary unit for filing the medical record number 44-37-98 is the last two digits, '98'. These terminal digits determine the initial filing sequence.
Step-by-step explanation:
In a terminal digit filing system, the medical record number 44-37-98 would be primarily filed under the last two digits, known as the terminal digits. Thus, the primary unit for filing this medical record would be 98. This number 98 would be used first to determine its sequence among other files, followed by the secondary unit (37 in this case), and finally the tertiary unit (44). These numbers help to spread out the files evenly across the filing system, making it more efficient for retrieval and minimizing the potential for filing errors.