Final answer:
The roll microfilm format is inefficient for multiple patient admissions due to the difficulty in retrieving information. The unit-numbering system is more suitable as it allows for easier access to a patient's complete medical history.
Step-by-step explanation:
The microfilm format that is considered inefficient when patients have multiple admissions on microfilm is B)roll. This system stores patient records in a continuous roll of film, which can be cumbersome when trying to retrieve information from multiple admissions. In contrast, the unit-numbering system is more efficient in this scenario because it assigns a unique number to a patient, and all of that patient's records are filed under this single number, allowing for easier access to the complete medical history.