The following excerpt is from "Throwing the Book at Apple" (Wall Street Journal, Review and Outlook, June 12, 2013): At the time, prior to the existence of the tablet device market that Jobs created with the iPad, Apple did not sell eminus−books. Amazon sold nine of every 10. Justice claims Jobs then forced Amazon and every other eminus−book distributor to adopt a new eminus−book pricing model that harmed consumers. Yet the average retail price for "trade" eminus−books has since dropped to $7.34 from $7.97, and Amazon's Kindle is still the industry leader with Apple trailing in third. Over the same period readers bought 447% more eminus−books, and they can choose from dozens of tablets for titles and other media content.
What market structure best describes the e - book market?
A. A monopoly
B. A perfectly competitive market
C. A competitive market with a few dominant firms producing identical goods
D. A competitive market with a few dominant firms producing substitutes

D. A competitive market with a few dominant firms producing substitutes

Explanation:

E book market has few dominant firms - Amazon, Apple.

Their e - book selling digital services have uniquely different features from each other. They serve similar nature of good ie e books contests. So, the digital services rendered by firms are substitute of each other.

Providing substitute goods, firms compete with each other.

As per technical economic terminologies : this market structure is analogous to Oligopoly market structure.

answer: marginal utility of the fourth brownie is 0.

explanation: marginal utility is the addtional utility gained from the consumption of one more unit of a good. it is given by,

so, marginal utility at the 4th unit will be given by

since, the values are not given here, you can simply find marginal utility at fourth unit by subtracting total utility at 3rd unit from total utility at 4th unit.

a bag with lamp

explanation:

because when in dark, our handbag would be hard to find, so when we switch on the light using thw remote, the bag would be easy to find