When the passengers are on board, what should the cabin attendants carry out?

A. direct the passengers to their seats
B. check passengers' hand luggage and other carry-on belongs
C. check all the seat belts and seat positions
D. perform safety demonstration
E. Change seats for passengers if necessary
F. Upgrade the passengers at their requests
G. Check if someone sitting near the exit is able to open the door in an emergency
H. Check all the seat belts and seat positions;
I. offering food and drinks