Which of the Following Statements Is Incorrect About Baking Powder

Which of the following statements is incorrect about baking powder?

A) Baking powder can be made by combining ¼ teaspoon of baking soda with ½ teaspoon of cream of tartar.
B) Federal standards require that all baking powders must be formulated to be able to produce at least 12% carbon dioxide when water and heat are applied.
C) Fast- or single-acting powder is available only to commercial bakers.
D) Double-acting baking powder reacts once when it is moistened and again during heating.
E) Fast- or single-acting baking powder mixtures should be allowed to stand for at least 15 minutes before being placed in the oven because carbon dioxide is produced as soon as water is added.