Which of the following is right?

Which of the following is right?
A Could you tell me when he has been away
B There are many students want to donate money to the victims
C i hope you to help us organize the charity sale
D we were told that sound travels through air
The 2008 earthquake was the _______ in chinese history (dead)
Scientists can not predict an earthquake exactly
Scientists are ______ _______ predict an earthquake exactly