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.

[EX Q]: Sentence1: keeping food cold is used for keeping food fresh. 
Sentence2: Keeping food cold is used to keep food simple and natural as possible.
[EX A]: cold

[EX Q]: Sentence1: Skin color is another polygenic trait. 
Sentence2: Skin color is influenced by multiple genes.
[EX A]: Skin

[EX Q]: Sentence1: Sound waves are longitudinal waves. 
Sentence2: telephones are used for communication by two people by transmitting waves.
[EX A]:
waves