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 had to swim from male to female reproductive organs for fertilization. 
Sentence2: If fertilized, the egg implants itself in the uterus.

SOLUTION: fertilization

PROBLEM: Sentence1: faulting of rock in Earth 's crust causes earthquakes. 
Sentence2: fault movement forms earthquakes.

SOLUTION: earthquakes

PROBLEM: Sentence1: Evolution is a change in the characteristics of living things over time. 
Sentence2: environment  can cause evolution.

SOLUTION:
Evolution