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: Lymphocytes are the key cells involved in the immune response. 
Sentence2: The key cells involved in the immune response produce antibodies.

SOLUTION: cells

PROBLEM: Sentence1: Endospores are commonly found in soil and water. 
Sentence2: Some bacteria form resistant cells called endospores.

SOLUTION: Endospores

PROBLEM: Sentence1: Human viruses are created by natural process. 
Sentence2: Something created by a natural process  cause many human diseases.

SOLUTION:
created