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: Many corals secrete an exoskeleton that builds up to become a coral reef. 
Sentence2: Good examples are Bubble coral, Elegance coral, Frogspawn and other Euphyllia corals.
[A]: coral


[Q]: Sentence1: keeping food cold is used for keeping food fresh. 
Sentence2: Keeping food at 40 degrees F or lower is used for keeping food fresh.
[A]: food


[Q]: Sentence1: Algae play significant roles as producers in aquatic ecosystems. 
Sentence2: An ecosystem includes the organisms and their habitat.
[A]:
ecosystems