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: exercise increases a body 's strength. 
Sentence2: Exercise is more than running and lifting.

SOLUTION: exercise

PROBLEM: Sentence1: harming an animal species has a negative impact on the population size of that species. 
Sentence2: Pesticides have a negative impact on the population size of a species.

SOLUTION: impact

PROBLEM: Sentence1: a greenhouse is used to protect plants from the cold. 
Sentence2: Greenhouse plants grow healthier.

SOLUTION:
greenhouse