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: lightning can cause a forest fire. 
Sentence2: Lightning can cause a natural cycle in forests.

SOLUTION: lightning

PROBLEM: Sentence1: Insulin is a hormone that helps cells absorb sugar from the blood. 
Sentence2: the pancreas produces a hormone that helps cells absorb sugar from the blood.

SOLUTION: absorb

PROBLEM: Sentence1: the emission of sulfur dioxide causes acid rain. 
Sentence2: The emission of sulfur dioxide causes pollution to the environment.

SOLUTION:
dioxide