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 Q]: Sentence1: Examples of gametes are ova and spermatozoa. 
Sentence2: fertilization of ova and spermatozoa produces a diploid zygote.
[EX A]: ova

[EX Q]: Sentence1: Any antigen that causes an allergy is called an allergen. 
Sentence2: molds are antigens.
[EX A]: antigen

[EX Q]: Sentence1: Secondary growth occurs in the lateral meristems. 
Sentence2: the area where secondary growth  occurs is located within and around the vascular tissues.
[EX A]:
Secondary