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: Producers use energy and inorganic molecules to make food. 
Sentence2: Green plants use energy and inorganic molecules to make food.
energy

Sentence1: an animal requires warmth for survival. 
Sentence2: Light and heat and warmth are basic necessities for survival.
warmth

Sentence1: Algae play significant roles as producers in aquatic ecosystems. 
Sentence2: algae plays significant roles as food in acquatic ecosystems.

Algae