The answer is D. Park.
A platform is a raised structure on which people stand to wait for a train or bus. A dock is a structure built out into the water to provide a place for boats to moor. A bus-stand is a place where buses stop to pick up and drop off passengers. A park is an area of land set aside for recreation, usually with trees, grass, and other plants.
The word “park” is different from the rest because it is the only word that is not associated with transportation. The other words are all associated with transportation, either as places where people wait for transportation or as places where transportation stops.