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: Fertilization is the penetration of the egg by a sperm. 
Sentence2: Sperm must swim from the male to the female egg.
[A]: egg


[Q]: Sentence1: An example of a cartilaginous fish is a shark. 
Sentence2: jaws make sharks excellent predators.
[A]: shark


[Q]: Sentence1: Prokaryotes All bacteria are prokaryotes. 
Sentence2: bacteria are single-celled organisms that lack a nucleus.
[A]:
bacteria