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 an object to lose energy. 
Sentence2: Friction occurs when surfaces rub together.

SOLUTION: friction

PROBLEM: Sentence1: erosion causes a river to become deeper and wider. 
Sentence2: On the contrary, the NILE is the longest river in Africa.

SOLUTION: river

PROBLEM: Sentence1: poison causes harm to living things. 
Sentence2: Poison causes things to die and quickly decay.

SOLUTION:
causes