Complex sentence: The bomb exploded from the middle carriage of a three carriage train that was was in the process of leaving Maelbeek/Maalbeek on its way to Arts-Loi/Kunst-Wet metro station.
Split into simpler sentences: The bomb exploded from the middle carriage of a three carriage train. The train was traveling between Maelbeek/Maalbeek and Arts-Loi/Kunst-Wet metro station.