The teenage market is a market that is categorized in what way?
a. by commodity
b. by price
c. by location
d. by consumer

The answer is option d.
The teenage market is a market that is categorized by consumer way.
we can say this because consumer means what you use or what you like to you use. These days teenagers like to eat fast food and go out with friends to enjoy and eat. so if you market a fast food shop, it means you are looking at the consumer way. That is why d is the best option.