Final answer:
In a terminal-digit numeric filing system, the medical record labeled a) 01-23-45 should be filed first as it has the smallest number ('45') in the last group of digits.
Step-by-step explanation:
In a terminal-digit numeric filing system, medical records are filed by the last group of numbers first, then the middle, and finally the first group. Considering the options provided, let's break down the last digits: a) 45, b) 56, c) 67, d) 78. The correct order of filing would start with the smallest last group of numbers, so the medical record to be filed first is a) 01-23-45, because '45' is the smallest number in the last group among the options provided.