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: high pressure systems cause clear weather. 
Sentence2: Weather Clear weather usually means good visibility.

SOLUTION: clear

PROBLEM: Sentence1: lightning can cause a forest fire. 
Sentence2: Lightning can cause a natural cycle in forests.

SOLUTION: lightning

PROBLEM: Sentence1: Immunity results from immunization. 
Sentence2: Resistance to disease results from getting shots.

SOLUTION:
Immunity