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: ultraviolet light causes sunburn. 
Sentence2: Sunburn risk is higher at elevation.

A: sunburn
****
Q: Sentence1: cell division often causes growth. 
Sentence2: Cell division leads to reproduction.

A: cell
****
Q: Sentence1: Heat is Energy and is measured in Joules. 
Sentence2: boiling means changing from liquid to a gas by adding joules.

A:
Joules
****