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: microscope is used to see small things by biologists by making them appear bigger. 
Sentence2: Something invented by Leeuwenhoek is used to see small things by biologists by making them appear bigger.

A: appear
****
Q: Sentence1: burning fossil fuels increases the carbon in the atmosphere. 
Sentence2: the byproduct of fossil fuels is carbon.

A: carbon
****
Q: Sentence1: a delta is formed by deposition of sediment at the mouth of a river by water fanning out. 
Sentence2: When the river slows, it drops the sediment in a wide fan, a delta.

A:
delta
****