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: mountains are formed by earthquakes. 
Sentence2: Mountains are formed by moving plates.

SOLUTION: are

PROBLEM: Sentence1: Warm temperatures have helped plant growth and sizing. 
Sentence2: a greenhouse helps  plant growth.

SOLUTION: growth

PROBLEM: Sentence1: Many species dig burrows in the ground. 
Sentence2: platypus females lay their eggs in the ground.

SOLUTION:
ground