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: Sperm pass out of the body through the urethra. 
Sentence2: Sperm travel from the testicles through the vas deferens to the seminal vesicles and the prostate.

SOLUTION: Sperm

PROBLEM: Sentence1: pathogens can cause disease. 
Sentence2: pathogens affects the immune system.

SOLUTION: pathogens

PROBLEM: Sentence1: sunlight and rain can cause a rainbow. 
Sentence2: All deserts have very little rain.

SOLUTION:
rain