Once a year people take part in Lights activity to help save energy.A. Show offB. Tum of

问题补充：

Once a year, people take part in Lights activity to help save energy.

A. Show off

B. Tum off

C. Take off

D. Put off

答案：

A. Show off

(答案→)B. Tum off

C. Take off

D. Put off

解析：句意：一年一次，人们参力地球一小时活动去帮助节省能源。分析地球一小的内容是关灯一小时，只有第二项为关灯之意。故选B