TASK DEFINITION: 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.
PROBLEM: Sentence1: Smoking accelerates the aging process. 
Sentence2: smoking accelerates the death of cells.

SOLUTION: Smoking

PROBLEM: Sentence1: Organisms cluster around hydrothermal vents in the ocean floor. 
Sentence2: vents on the ocean floor are powered by heat.

SOLUTION: vents

PROBLEM: Sentence1: Limestone is a type of sedimentary rock. 
Sentence2: flowing water can slowly dissolve carbon in limestone.

SOLUTION:
Limestone