In which area have Americans received the most awards（）

A. Can I help you
C. Safety belt, please.
E. Is there anything serious
G. What flight are you taking
B. We are taking off at last.
D. The engine went wrong.
F. Just a moment, please.
H. It should be OK in an hour.

A．building bridges across them
B．driving generators into them
C．building dams across them
D．directing them into homes and factories