Which situation is the best example of a zero sum game?

The correct answer is D) Every purchase you make at a chain store is a sale that a local small business misses out on.

The situation that is the best example of a zero-sum game is "Every purchase you make at a chain store is a sale that a local small business misses out on."

In the Theory of Games, a zero-sum game is when one person's gain means that another person loses something, and at the end when someone wins and other loses, there is a zero-sum game. So when you purchase something in a big supermarket chain, small and the family business loses, meaning that the small store won't be able to sell you what you just bought.

The question and options are attached in the picture below.  

we would need to be able to read the passage in question to determine which factor allowed david believe he could defeat goliath. post the passage, and i'd love to out.