Which of the following statements by Tom demonstrates that his buying plans obey the law of demand? O A. The only thing that's changed is the price of textbooks: they've become more expensive and now I'm not buying as many O B. I can't afford as many textbooks because my rent has increased. OC. At an average price of $80 per text book, I plan to buy 5 text books per semester OD. For me, a good course website is a substitute for a textbook.