Which of the following statements is not true?

a. electronically linking equity dealers and exchange markets is slowly leading toward a national market system

b. electronically linking international markets has created 24-hour trading oppourtunities for some stocks

c. U.S stock exchanges have extended (after hours) their normal trading hours in which shares are traded electronically, linking U.S with the hours of international marketsin.

d. All of the above statements are true