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: Examples of gametes are ova and spermatozoa. 
Sentence2: fertilization of ova and spermatozoa produces a diploid zygote.
[A]: ova


[Q]: Sentence1: Mitosis is cell division. 
Sentence2: mitosis often causes growth.
[A]: Mitosis


[Q]: Sentence1: Nausea and vomiting are caused by activation of the vomiting center in the brain. 
Sentence2: the brain is responsible for removing toxic material from the stomach.
[A]:
brain