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: Female monotremes lack a uterus and vagina. 
Sentence2: Babies are normally delivered from the uterus through the vagina.
[EX A]: uterus

[EX Q]: Sentence1: All chemical reactions require activation energy to get started. 
Sentence2: Catalysts lower the activation energy.
[EX A]: activation

[EX Q]: Sentence1: Reproduction is the process by which organisms give rise to offspring. 
Sentence2: Humans are complex organisms.
[EX A]:
organisms