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.

Example Input: Sentence1: evaporation can be used for separating a solute from a solvent in a solution. 
Sentence2: Evaporation can be used for segregation a solute from a solvent in a solution.
Example Output: a

Example Input: Sentence1: Ferns are vascular plants. 
Sentence2: when a fern grows, its size of leaves may increase.
Example Output: Ferns

Example Input: Sentence1: Sweat wets the skin, and when it evaporates, it cools the body. 
Sentence2: Sweat is made of salt and water.
Example Output:
Sweat