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: when a hemisphere is tilted away from the sun , that hemisphere receives less direct sunlight. 
Sentence2: Sunlight is delivered in small packets of energy called photons.

SOLUTION: sunlight

PROBLEM: Sentence1: forming coal requires decaying vegetation. 
Sentence2: Forming fossil fuels requires decaying vegetation.

SOLUTION: decaying

PROBLEM: Sentence1: Most reptiles have good eyesight and a keen sense of smell. 
Sentence2: Geckos have good eyesight.

SOLUTION:
eyesight