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: Autumn brings the changing of the seasons. 
Sentence2: Earth 's tilt on its rotating axis causes autumn.

SOLUTION: Autumn

PROBLEM: Sentence1: Speciation events are thus examples of macroevolution. 
Sentence2: Speciation events occur over geologic time above the level of the species.

SOLUTION: Speciation

PROBLEM: Sentence1: transportation technology is used for moving people. 
Sentence2: Cars can kill people or they can transport people.

SOLUTION:
people