What must you heed in this situation?

Your answer is fully correct because in this situation, German traffic rules require you to pass the bus at walking speed only, and only if you are sure that no passengers are endangered.

This rule is important because people are getting on or off the bus, which means that sudden movements or speeds could cause danger to the passengers. Passing at walking speed allows you to react promptly if someone steps onto the road. At the same time, you must be certain that no passengers will be endangered during your passing.

The third option (not pass under any circumstances) is not correct here because passing is allowed under strict safety conditions.

In summary, always slow down to walking speed near bus stops when passengers might be boarding or leaving, and ensure you are absolutely sure it is safe to pass, protecting pedestrian safety.