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: Leeches are external parasites. 
Sentence2: Leeches live on the surface of their hosts.

SOLUTION: Leeches

PROBLEM: Sentence1: a pulley is used for lifting objects. 
Sentence2: Resistance exercises are weight-lifting exercises.

SOLUTION: lifting

PROBLEM: Sentence1: Nephrons are the structural and functional units of the kidneys. 
Sentence2: Each nephron contains a system of blood vessels and tubules.

SOLUTION:
Nephrons