Which of the Following Is a Reason for London's Dominance

Which of the following is a reason for London's dominance in the foreign exchange market?

A) Great Britain's decision to retain the British pound instead of using the euro,making the pound an important vehicle currency
B) The preeminence of Financial Times Stock Exchange (FTSE) index as an economic health indicator
C) London's geographical position making it the link between the East Asian and New York markets
D) London being the preferred headquarters location for major multinational corporations