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: For instance, glucose is a sugar. 
Sentence2: insulin helps cells take up sugar from the blood.

SOLUTION: sugar

PROBLEM: Sentence1: Rainy clouds cause rain, and excess water vapor from clouds is the basis of rainbows. 
Sentence2: Condensation can lead to rain.

SOLUTION: rain

PROBLEM: Sentence1: Biomass is the total mass of organisms at a trophic level. 
Sentence2: Each of the steps in the food chain is a trophic level .

SOLUTION:
level