Answer:
Rice is so cheap and truffles are so expansive because D. People eat so much rice that an additional serving of rice has little marginal value, but the marginal value of another serving of truffles is very high.
Explanation:
When it comes to tasty or nutritious foods, there should not be any reason to be more expensive than others food stuffs. However, they often cost a little more. Regarding rice and its easy way of cooking, it is not a strong argument to talk about the price. So the right answer D, due to the fact that is true that eating a higher rate of rice won't have such a great marginal value as it will with truffles. It has to do a lot with higher demand of rice.