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: friction causes the temperature of an object to increase. 
Sentence2: When we increase the temperature of objects, they always expand.

SOLUTION: increase

PROBLEM: Sentence1: erosion of soil has a negative impact on the environment. 
Sentence2: erosion of soil has a negative impact on forests.

SOLUTION: erosion

PROBLEM: Sentence1: navigation requires knowing direction. 
Sentence2: International shipping requires more than navigating foreign waters or air space.

SOLUTION:
navigation