As you know，it is my duty to________my younger sisters from being hurt when they are in danger.
A．prevent B．save C．stop D．protect
If no measures are taken, the special wild plant will ________ some day.
A．die out B．die away C．die down 
D．die off
Sir, you ________ take this seat. It’s just for the old.
A. won’t B. can’t C. oughtn’t to D. needn’t
He spoke as though he________ anything of the world.
--Really?
A. knew B. had known C. knows D. has know
As we know, the 2008 Olympic will________ in Beijing, China.
A. take place B. be taken place C. be to be held D. hold
The old man has two sons，________is a soldier.
A．one of whom B．both of them C．all of whom D．both of whom
