People have planted a great many trees in order to wind and sand in the desert.A. hold dow

问题补充：

People have planted a great many trees in order to wind and sand in the desert.

A. hold down

B. hold up

C. hold back

D. hold out

答案：

A. hold down

B. hold up

(答案→)C. hold back

D. hold out

解析：hold down压制，限制；hold up推迟，耽搁；hold back阻挡，抑制；hold out提供，提出。句意：人们种了大量的树，为了阴挡风和沙尘。由此可知答案为C项。