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: wind is used for producing electricity. 
Sentence2: Wind is caused because of pressure differences in the atmosphere.

A: wind
****
Q: Sentence1: when a hemisphere is tilted towards the sun , that hemisphere receives more direct sunlight. 
Sentence2: When a hemisphere is tilted towards the sun that hemisphere has higher temperatures.

A:
hemisphere
****