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: an automobile engine transforms chemical energy into mechanical energy. 
Sentence2: cars transform chemical energy into mechanical energy.

SOLUTION: chemical

PROBLEM: Sentence1: moss causes chemical weathering. 
Sentence2: Sphagnum moss mixed with peat moss.

SOLUTION: moss

PROBLEM: Sentence1: Evolution requires genetic diversity. 
Sentence2: Evolution requires sexual reproduction.

SOLUTION:
Evolution