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 circle graph can be used to display percents. 
Sentence2: pie charts are circle graphs.

A: circle
****
Q: Sentence1: Cells are the units of function in living things. 
Sentence2: living things cannot survive without oxygen.

A: living
****
Q: Sentence1: electricity is used as an energy source by electrical devices. 
Sentence2: Computers use electricity as an energy source.

A:
electricity
****