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: cold fronts cause thunderstorms as they pass by. 
Sentence2: Cold fronts cause lightning.

SOLUTION: cold

PROBLEM: Sentence1: Mammals that are viviparous are called therian mammals. 
Sentence2: Mouse-sized viviparous mammals evolved by Jurassic times.

SOLUTION: Mammals

PROBLEM: Sentence1: boiling is when liquids are heated above their boiling point. 
Sentence2: Heating liquids above a certain temperature converts to gas.

SOLUTION:
heated