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: Babies that are very large or very small at birth are less likely to survive. 
Sentence2: Babies that are very large or very small at birth are less likely to live.
Example Output: Babies

Example Input: Sentence1: Apollo 13 spacecraft is launched. 
Sentence2: Propulsion was used for flying Apollo 13.
Example Output: 13

Example Input: Sentence1: Female gametophytes produce eggs inside the ovaries of flowers. 
Sentence2: All gametophytes are haploid.
Example Output:
gametophytes