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: Any antigen that causes an allergy is called an allergen. 
Sentence2: Allergens can trigger asthma attacks.

SOLUTION: allergen

PROBLEM: Sentence1: triceps contracting causes a person 's elbow to straighten. 
Sentence2: muscles contracting cause a person's elbow to straighten.

SOLUTION: contracting

PROBLEM: Sentence1: the emission of sulfur dioxide causes acid rain. 
Sentence2: Burning coal causes acid rain.

SOLUTION:
acid