We have planted many trees in order to wind and sand in the desert.A. hold downB. hold upC

问题补充：

We have planted 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：题意：我们种了大量的树，为了阴挡风和沙尘。hold down压制，限制；hold up推迟，耽搁；hold back阻挡，抑制；hold out提供，提出。