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: moss causes chemical weathering. 
Sentence2: Sphagnum moss mixed with peat moss.

SOLUTION: moss

PROBLEM: Sentence1: Energy enters ecosystems in the form of sunlight or chemical compounds. 
Sentence2: Energy enters ecosystems in the form of photons.

SOLUTION: Energy

PROBLEM: Sentence1: soil is formed by weathering. 
Sentence2: Weathering is the breakdown of rock.

SOLUTION:
weathering