The correct answer is - d. France.
France is the only European country that has access to the Atlantic Ocean, Mediterranean Sea, and North Sea.
France's coastline on the Atlantic Ocean is on its western side, and it is the biggest coastline of the three, with one of the most important ports being Nantes. \
The coastline on the Mediterranean Sea is on the south of the country, with Marseilles being the major port.
The coastline on the North Sea is located on the north of the country, and the biggest port is Calais.