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.

[Q]: Sentence1: Fertilization is the penetration of the egg by a sperm. 
Sentence2: Sperm must swim from the male to the female egg.
[A]: egg


[Q]: Sentence1: Coral Reefs Coral reefs are widely distributed in warm shallow waters. 
Sentence2: warm shallow waters provide food and shelter to many ocean organisms.
[A]: shallow


[Q]: Sentence1: photosynthesis means producers convert from carbon dioxide, water, and solar energy into carbohydrates for themselves. 
Sentence2: Photosynthesis is the chemical change that produces food and oxygen in green plants.
[A]:
photosynthesis