问题补充:
People have planted a lot of trees and grass 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:人们种了大量的树和草,为了阻挡风沙。