Correct Option: D

The Channel Tunnel is a 50.5-kilometre (undersea rail tunnel linking Folkestone, Kent, in the United Kingdom with Coquelles, Pas-de-Calais, near Calais in northern France beneath the English Channel at the Strait of Dover. At its lowest point, it is 75 m (250 ft) deep. At 37.9 kilometres, the Channel Tunnel possesses the longest undersea portion of any tunnel in the world, although the Seikan Tunnel in Japan is both longer overall at 53.85 kilometres.