Conclusion I: The train driver should not be immediately suspended without a thorough investigation. The cause of the accident may not be the driver's fault, so this conclusion does not follow.
Conclusion II: The driver of the bus should be tried in court for negligence. This follows logically, as the bus driver is responsible for ensuring safety at level crossings.
Conclusion III: The railway authority should indeed be asked to man all its level crossings to enhance safety and prevent such accidents in the future. This conclusion also follows.
So, the correct option is (D): Only II and III follow.