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.
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Question: Sentence1: erosion of soil has a negative impact on the environment. 
Sentence2: erosion of soil has a negative impact on forests.

Answer: erosion


Question: Sentence1: electric devices require electrical energy to function. 
Sentence2: Lie detectors are electrical or mechanical devices.

Answer: devices


Question: Sentence1: Immunodeficiency occurs when the immune system is not working properly. 
Sentence2: immunodeficiency causes people to take longer to get well.

Answer:
Immunodeficiency