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.

Sentence1: Cells are the units of function in living things. 
Sentence2: living things cannot survive without oxygen.
living

Sentence1: Erosion of rock makes nutrients available. 
Sentence2: rain causes nutrients to be available.
nutrients

Sentence1: Humans have collected and grown mushrooms for food for thousands of years. 
Sentence2: Humans have collected and grown fungus for food for thousands of years.

Humans