What must a Marijuana Worker Permit holder carry while on duty?

Answer: C — Their valid Marijuana Worker Permit

A Marijuana Worker Permit holder is required to carry their valid Marijuana Worker Permit while on duty to ensure compliance with Oregon's regulations. This permit serves as official documentation that the individual is legally authorized to work in the regulated marijuana industry. Carrying the permit helps to verify their identity and qualification in case they are inspected by authorities or if there is a need to demonstrate their legal status within the establishment. The other options do not fulfill this regulatory requirement. While having an employee handbook or customer service training certificate could be beneficial in their job role, they are not required to be carried at all times. A smartphone, although useful for communication, is not a legal requirement and does not serve as verification of the individual's permit status. Thus, carrying the valid Marijuana Worker Permit is essential for proper compliance and operation within the cannabis industry.