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.

[EX Q]: Sentence1: ultraviolet light causes sunburn. 
Sentence2: Sunburn risk is higher at elevation.
[EX A]: sunburn

[EX Q]: Sentence1: Amphibians are the first true tetrapods, or vertebrates with four limbs. 
Sentence2: Frogs are classified as amphibians.
[EX A]: Amphibians

[EX Q]: Sentence1: Colloidal systems are suspensions of solid matter in liquids. 
Sentence2: melting is when something part of a colloidal system is heated above its melting point.
[EX A]:
Colloidal