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: Generally, pheromones are volatile substances. 
Sentence2: Male dogs use volatile substances in urine to mark their territory.

SOLUTION: substances

PROBLEM: Sentence1: mineral graphite is used for making pencil lead. 
Sentence2: Diamond and graphite are made of carbon.

SOLUTION: graphite

PROBLEM: Sentence1: Flowing water can slowly dissolve carbon in sedimentary rock. 
Sentence2: Flowing water can slowly dissolve carbon in sandstone.

SOLUTION:
Flowing