TASK DEFINITION: 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.
PROBLEM: Sentence1: an image in a mirror is formed by reflecting light. 
Sentence2: mirrors can be seen with our eyes.

SOLUTION: mirror

PROBLEM: Sentence1: Skin color is another polygenic trait. 
Sentence2: Skin color is influenced by multiple genes.

SOLUTION: Skin

PROBLEM: Sentence1: Introns are regions that do not code for proteins. 
Sentence2: Protein There are many types of protein.

SOLUTION:
proteins