The distance from the airport to the center of Sydney is______.

A．indicate the theme of the passage
B．explain why every group has a culture of its own
C．introduce the similarity of non-superiority in culture and language
D．start up the speech

A．He has been in America for three years.
B．He has always lived in America.
C．He visited America three years ago.
D．He has come to America to do research on advertising.