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: the moon revolving around the Earth causes the phases of the moon. 
Sentence2: Lets start our discussion of the Moon's phases with the New Moon phase.

SOLUTION: phases

PROBLEM: Sentence1: Most bryophytes are small. 
Sentence2: Most in the same group as mosses are small.

SOLUTION: small

PROBLEM: Sentence1: a calculator is used for adding. 
Sentence2: Calculator Use an online calculator.

SOLUTION:
calculator