What is the right thing to do in this situation?

Your answer is correct because, according to German traffic rules, when passing a bus that is stopped at a bus stop, you must proceed at walking speed (Schritttempo). This rule ensures the safety of passengers who may be boarding or alighting, especially children or elderly people who might suddenly step onto the roadway. Maintaining a very low speed gives you enough time to react to any unexpected situations near the bus.

The other options are incorrect because the car that is stopped or about to pull out does not necessarily have to stop if it is not required by traffic signs or signals, and you are not allowed to continue at the same speed when passing a stopped bus, as this would endanger pedestrians and other road users near the bus. Therefore, reducing speed to walking pace when passing a stopped bus is mandatory for safety and to comply with §20 StVO (German Road Traffic Regulations).