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: Tree-ring dating the 1700 Cascadia earthquake. 
Sentence2: estimating the age of trees can be used in reviewing earthquake history.

SOLUTION: earthquake

PROBLEM: Sentence1: threatening behavior by predators causes a porcupine to extend its quills. 
Sentence2: Fishers are one of the few specialized predators on porcupines.

SOLUTION: predators

PROBLEM: Sentence1: Reef-building corals are hermatypic. 
Sentence2: Hermatypic organisms provide food and shelter to many ocean organisms.

SOLUTION:
hermatypic