In order to let more people pay attention to their plan they some signs on the wall. A.

问题补充：

In order to let more people pay attention to their plan, they some signs on the wall.

A. put on

B. put up

C. set up

D. give up

答案：

A. put on

(答案→)B. put up

C. set up

D. give up

解析：句意：为了让更多的人注意他们的计划，他们在墙上挂起了一些牌子。put on穿上；put up挂起；set up建立；give up 放弃。故选B。