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.

Sentence1: An organism can gain energy by assimilation or absorption of food. 
Sentence2: Organisms require food for growth.
food

Sentence1: Eggs are usually laid in a nest. 
Sentence2: birds have nests.
nest

Sentence1: heating salt water causes the water to evaporate while the salt remains. 
Sentence2: When water evaporates, salts in the water remain and become more concentrated.

water

