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: Polygenic inheritance Polygenic traits are controlled by an unknown number of genes. 
Sentence2: Skin color is inherited from a number of genes.
[A]: genes


[Q]: Sentence1: Acids dissolve in base and turn blue litmus red. 
Sentence2: acid changes color.
[A]: Acids


[Q]: Sentence1: Lymph fluid is rich in protein. 
Sentence2: A protein-rich fluid leaks into spaces between cells.
[A]:
protein