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: a flashlight converts chemical energy into light energy. 
Sentence2: Only as long as there are batteries in the flashlight, the flashlight will function.

SOLUTION: flashlight

PROBLEM: Sentence1: Habitat destruction is the primary cause of extinction or threat of extinction for all animals. 
Sentence2: building housing developments may cause extinction.

SOLUTION: extinction

PROBLEM: Sentence1: Rainfall is more at the tropics and on windward side of mountains. 
Sentence2: Rainfall falls on the windward side.

SOLUTION:
Rainfall