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: friction is used for stopping a vehicle by brakes. 
Sentence2: friction is used for stopping a car by brakes.

SOLUTION: brakes

PROBLEM: Sentence1: Cell death occurs by activation of cell death genes. 
Sentence2: Aging is associated with the activation of certain genes.

SOLUTION: activation

PROBLEM: Sentence1: ultraviolet light causes sunburn. 
Sentence2: ultraviolet light causes skin redness and pain, possible swelling, blisters, fever, headaches.

SOLUTION:
causes