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: Mitosis is cell division. 
Sentence2: mitosis often causes growth.

SOLUTION: Mitosis

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

SOLUTION: graphite

PROBLEM: Sentence1: Coral is the calcite shell of the coral animal. 
Sentence2: animals with calcite shells form large colonies in shallow tropical water.

SOLUTION:
animal