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: riding a bike does not cause pollution. 
Sentence2: riding a bike does not release particles.

SOLUTION: bike

PROBLEM: Sentence1: Rivers, rainwater, well water and most lakes contain fresh water. 
Sentence2: canyons are formed by rainwater.

SOLUTION: rainwater

PROBLEM: Sentence1: volcanic ash in the atmosphere decreases the temperature by blocking the sun. 
Sentence2: Or a veil of tiny particles from a volcanic eruption can block the sun.

SOLUTION:
volcanic