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: burning fossil fuels increases the carbon in the atmosphere. 
Sentence2: the byproduct of fossil fuels is carbon.
carbon

Sentence1: Sound vibrations travel at different speeds through different materials. 
Sentence2: the type of material through which sound passes changes the sound vibrations.
Sound

Sentence1: a spider web is used to capture food by spiders. 
Sentence2: Crab spiders spin no webs.

spider