If an interrupted white light glows at a railway crossing safety device, a driver is obliged
a) in a distance of 30 m in front of a railway crossing and when passing through it, to drive with maximum speed 30 km/h,
b) to stop a vehicle,
c) in a distance of 50 m in front of a railway crossing and when passing through it,
to drive with maximum speed 50 km/h,
