When is a bus driver not allowed to drive?

The selected combination is correct because all three scenarios outlined are valid reasons under German traffic regulations that prohibit a bus driver from operating a vehicle.

1. Suffering from a notifiable contagious disease poses a risk not only to the driver but also to passengers and others on the road, therefore, it is essential that the driver refrains from driving to ensure public safety.
2. If a member of his household has a notifiable contagious disease, this may also increase the risk of transmission and indirectly affect the driver's ability to operate the bus safely.
3. Being seriously indisposed may affect a driver's judgement, reaction time, and overall ability to safely control a vehicle, which is critical for the safety of all road users.

Hence, it is vital for bus drivers to meet health standards to ensure they can operate their vehicles safely and responsibly.