Final answer:
Officers whose apparatus use more than 15% of the mix within a 12-month period are required to report the problem and schedule their apparatus for diagnostic testing. The correct answer is C. 15%, required, 12-month.
Step-by-step explanation:
The correct answer is C. 15%, required, 12-month.
According to the information provided, officers whose apparatus (presumably referring to equipment) use more than 15% of the mix within a 12-month period are required to report the problem to the specified authority and schedule their apparatus for diagnostic testing.
Therefore, any usage of the mix exceeding 15% within a 12-month period must be reported and investigated.