When performing the occasional carriage of passengers, what document must you present for inspection by the competent persons upon demand?

You answered correctly. For occasional carriage of passengers (known as "Gelegenheitsverkehr" in Germany), you must present both the registration certificate Part I and the approval for occasional carriage of passengers if requested by authorized persons. The registration certificate Part I confirms the vehicle’s legality and registration, while the special approval proves you are legally allowed to carry passengers occasionally for hire. The passenger accident insurance certificate is not required to be shown in this situation. Understanding which documents are required ensures you comply with regulations during checks.