问题补充:
When you come into the exhibition hall,you can see a large board with a notice on it,saying visitorsnot to touch the exhibits.
A. will request
B. request
C. are requesting
D. are requested
答案:
A. will request
B. request
C. are requesting
(答案→)D. are requested
解析:“request sb.(not)to do sth.要求某人(不要)做某事”是固定结构,根据题干,应使用被动语态。