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: Animals behave in a variety of ways which enhance their chances of survival and reproduction. 
Sentence2: Animals learn to behave to increase chances of survival.

A: behave
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Q: Sentence1: weathering means breaking down rocks from larger whole into smaller pieces by weather. 
Sentence2: Trash collectors work in all types of weather, including rain and snow.

A: weather
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Q: Sentence1: Running water is better able to dissolve oxygen and nutrients than standing water. 
Sentence2: Large, warm rivers hold populations but few occur in cold running water.

A:
Running
****