What must you do after completing a trip for an interstate carrier?

Answer: B — Complete an after trip inspection report

Completing an after trip inspection report is essential for ensuring that the vehicle is safe and in good working condition for future trips. This report serves as a record of the vehicle's condition, documenting any issues or maintenance needs that may have arisen during the trip. It helps to identify potential safety concerns before the next use and ensures compliance with regulations that govern vehicle maintenance and safety checks. While submitting a driving log, delivering a passenger report, or cleaning the bus interior are important tasks associated with end-of-trip procedures, they don't specifically focus on the immediate assessment of the vehicle's condition. The after trip inspection report is a critical component of maintaining safety standards in passenger transport, making it the correct answer.