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: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Water freezes into ice when cooled.

SOLUTION: freezes

PROBLEM: Sentence1: Some herbivores have more than one stomach. 
Sentence2: Camels are an herbivore.

SOLUTION: herbivores

PROBLEM: Sentence1: Antibodies are protein molecules. 
Sentence2: Plasma cells are activated B cells that secrete protein molecules.

SOLUTION:
molecules