The correct options are
A Poor conditions of trains and tracks
B Overspeeding on sharp turns
D Disruption of railway network
Derailments can occur due to poor maintenance of trains and tracks, human error, and due to plain sabotage. If the loco pilot of the train over speeds at sharp turns, there is a possibility of losing control of the train. This would result in the train running off the tracks. Sometimes, people knowingly disrupt the rail transport network; it is called sabotage.