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 Input:
Sentence1: melting is when solids are heated above their melting point. 
Sentence2: Ice is a solid, it's cold and it's hard.

Ex Output:
solids


Ex Input:
Sentence1: Mutations are essential for evolution to occur. 
Sentence2: Genes are altered for evolution to occur.

Ex Output:
evolution


Ex Input:
Sentence1: Plants release oxygen during the day but not during the night. 
Sentence2: Ferns are seedless vascular plants.

Ex Output:

Plants