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: Temperature Scales Temperature is the energy of vibration. 
Sentence2: a thermometer is used to measure energy of vibration.

A: energy
****
Q: Sentence1: if soil is permeable then water easily flows through that soil. 
Sentence2: The increase in permeability is caused by the formation and expansion of ice in the soil.

A: permeable
****
Q: Sentence1: if a tree falls then sunlight becomes available to the surrounding plants. 
Sentence2: When a big tree falls, sunlight shines on smaller plants and they get a chance to grow.

A:
sunlight
****