40116
Usually , the timekeeping circuitry has a battery as a backup source for an uninterrupted power supply to keep the clock on time , while the projection light only works when the unit is connected to an A.C. supply .
 location: A.C.
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: A.C. 
Answer:
 location: A.C.