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: Complex chemistry is needed to carry out all the functions of life. 
Sentence2: Chemistry is primarily concerned with matter, energy, and their interactions.

SOLUTION: chemistry

PROBLEM: Sentence1: Eggs are usually laid in a nest. 
Sentence2: birds have nests.

SOLUTION: nest

PROBLEM: Sentence1: Vertebrate chordates have a backbone. 
Sentence2: Yep, lizards are chordates, just like humans.

SOLUTION:
chordates