问题详情：
The notice on the wall is meant to ________ the unwanted visitors, especially during working hours.
A. keep up B. keep off
C. keep from D. keep back
【回答】
B keep up“维持；继续”； keep off“离开；使不接近”； keep from“阻止；使免于”； keep back“阻挡；抑制”。根据句意，B项最佳。
知识点：动词
题型：选择题
