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: Coral reefs are made up of the accumulated exoskeletons of the coral polyp. 
Sentence2: coral polyps form reefs.
[A]: polyp


[Q]: Sentence1: a switch is used to start the flow of current in an electrical circuit. 
Sentence2: lights are on when there is flow of current in an electrical circuit.
[A]: circuit


[Q]: Sentence1: Direct sunlight increases temperature and evaporation rates at the soil and leaf surfaces. 
Sentence2: the temperature of the soil of a hemisphere cools down when tilted away from the sun.
[A]:
temperature