What is the primary factor you need to consider when selecting a method of transmission or transportation of classified material?

The primary factor to consider when selecting a method of transmission or transportation of classified material is the level of security required to protect the information from unauthorized access or interception. This includes evaluating the method's ability to safeguard against physical theft, electronic eavesdropping, and environmental threats. Additionally, compliance with relevant regulations and ensuring that personnel involved are properly vetted and trained in handling classified material are crucial considerations.