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: wind is used for producing electricity. 
Sentence2: Winds are caused by pressure differences.

A: wind
****
Q: Sentence1: Antigens are proteins foreign to the body. 
Sentence2: antigens are proteins.

A: proteins
****
Q: Sentence1: When a substance melts, it changes phase from a solid to a liquid by the application of heat. 
Sentence2: Changing the phase of a solid can be done by adding heat energy.

A:
changes
****