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 microscopic building blocks of organisms. 
Sentence2: proteins are the building blocks of organisms.
organisms

Sentence1: Limestone caves displaying stalactites. 
Sentence2: Limestone caves are formed by depositions.
Limestone

Sentence1: creating paper requires cutting down trees. 
Sentence2: Reductions in paper production would help stop global warming.

paper