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: An organism can gain energy by assimilation or absorption of food. 
Sentence2: Organisms require food for growth.

SOLUTION: food

PROBLEM: Sentence1: Acids dissolve in base and turn blue litmus red. 
Sentence2: acid changes color.

SOLUTION: Acids

PROBLEM: Sentence1: Sperm had to swim from male to female reproductive organs for fertilization. 
Sentence2: If the egg is fertilized, it can implant in the uterus and cause pregnancy.

SOLUTION:
fertilization