Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

[Q]: Sentence1: a battery converts chemical energy into electrical energy. 
Sentence2: Battery electricity comes conversion.
[A]: battery


[Q]: Sentence1: a circle graph can be used to display percents. 
Sentence2: pie charts are circle graphs.
[A]: circle


[Q]: Sentence1: a switch is used to start the flow of current in an electrical circuit. 
Sentence2: Some systems have an additional connection for a second doorbell switch.
[A]:
switch