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: Earthquakes are natural disasters. 
Sentence2: earthquakes can cause animals to leave an environment.

A: Earthquakes
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Q: Sentence1: Female monotremes lack a uterus and vagina. 
Sentence2: Babies are normally delivered from the uterus through the vagina.

A: uterus
****
Q: Sentence1: a breathing mask is used for keeping harmful particles from entering the respiratory system. 
Sentence2: When inhaled, the particles lodge in the respiratory system, causing or aggravating health problems.

A:
respiratory
****