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: Bees feed on nectar and pollen. 
Sentence2: Plant reproduction often requires bees and nectar.

SOLUTION: Bees

PROBLEM: Sentence1: Gravity is a force that pulls on things. 
Sentence2: A force that pulls on things pulls objects towards planets.

SOLUTION: force

PROBLEM: Sentence1: a balance is used for measuring mass of an object. 
Sentence2: a balance is used for measuring grams of an object.

SOLUTION:
balance