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: Plants use unsaturated fatty acids to store energy. 
Sentence2: Plants and fish contain fatty acids.

SOLUTION: Plants

PROBLEM: Sentence1: Batteries are a better source of DC electricity. 
Sentence2: a flashlight requires batteries to produce light.

SOLUTION: Batteries

PROBLEM: Sentence1: a vehicle is used for transportation. 
Sentence2: motorcycles are used for transportation.

SOLUTION:
transportation