A few years ago, David had the idea of selling CDs over the Internet. He started his work from his home. Now he sells over 500,000 CDs a year and has made himself into a millionaire , at the age of 24. "I could see that this was the future of shopping," says David. "Why should you pay $15 for a CD and spend the time and the money going into the shop? You know sometimes you have to find a place for your car too. You can have the same CD for half of the price by clicking on your computer. And we can find any CD you want and bring it to your door in 24 hours!" David said this is the only beginning, "One day we'll do our shopping over the Internet: it's easier, quicker and cheaper. Shops and supermarkets will be the past." How has he become a millionaire? A) By making new supermarkets. B) By making advertisements. C) By selling ideas to others. D) By selling CDs on the Internet.
A:
D