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: Refraction is the bending of light. 
Sentence2: a rainbow is formed by bending of light by separating light into all different colors.

A: bending
****
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: Students take a field trip to an ecosystem to observe the homes of animals in natural habitats. 
Sentence2: Cutting down trees has a negative impact on the homes of animals  in natural habitats.

A:
animals
****