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: skin is used for protecting the body from harmful substances. 
Sentence2: Acids are harmful to tissue.

SOLUTION: harmful

PROBLEM: Sentence1: cell division often causes growth. 
Sentence2: Mitosis is cell division.

SOLUTION: cell

PROBLEM: Sentence1: And since infrared energy is heat, it warms the Earth. 
Sentence2: Fire converts chemical energy into light and warmth for earth.

SOLUTION:
Earth