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: Telephone Telephone calls are expensive. 
Sentence2: Communicating by transmitting sound is expensive.

A: expensive
****
Q: Sentence1: Humans have collected and grown mushrooms for food for thousands of years. 
Sentence2: Yeast and mushrooms are types of fungus.

A: mushrooms
****
Q: Sentence1: a solar panel converts sunlight into electricity. 
Sentence2: solar panels can power lasers.

A:
panel
****