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: Batteries are a better source of DC electricity. 
Sentence2: a flashlight requires batteries to produce light.

SOLUTION: Batteries

PROBLEM: Sentence1: igneous rocks are formed from magma cooling. 
Sentence2: magma solidifies into igneous rocks.

SOLUTION: magma

PROBLEM: Sentence1: cycles of freezing and thawing water cause ice wedging. 
Sentence2: Water is made up of H2O molecules.

SOLUTION:
water