Which of the Following Statements Is True

Multiple Choice

Which of the following statements is true?

A) The demand curve for a group of consumers in a market is simply the horizontal summation of each individual's demand.
B) The single demand curve shows the quantity of a good that people will buy, allowing all factors (price, income, expected future prices, etc.) to vary.
C) An increase in income will cause a person to move down and to the right along her demand curve.
D) All of the above are true.