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: a circle graph can be used to display percents. 
Sentence2: pie charts are circle graphs.

SOLUTION: circle

PROBLEM: Sentence1: Ground tissue makes up most of the interior of a plant. 
Sentence2: ground tissue makes up most of the interior of a dandelion.

SOLUTION: Ground

PROBLEM: Sentence1: darkness has a negative impact on photosynthesis. 
Sentence2: Plants feed themselves through the process called photosynthesis.

SOLUTION:
photosynthesis