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: Eggs are usually laid in a nest. 
Sentence2: birds have nests.

A: nest
****
Q: Sentence1: Skin color is another polygenic trait. 
Sentence2: Skin color is influenced by multiple genes.

A: Skin
****
Q: Sentence1: Solar energy is the energy in the sun's rays. 
Sentence2: the sun's rays can be used for heating a building by a heating system.

A:
rays
****