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.

[EX Q]: Sentence1: Ovulation is the release of an egg from an ovary. 
Sentence2: The release of an egg during ovulation is used in reproduction.
[EX A]: Ovulation

[EX Q]: Sentence1: Producers use energy and inorganic molecules to make food. 
Sentence2: Green plants use energy and inorganic molecules to make food.
[EX A]: energy

[EX Q]: Sentence1: keeping food cold is used for keeping food fresh. 
Sentence2: Refrigerators are suppose to add coldness to the food inside of it.
[EX A]:
cold