Rice cakes have
a lot of carbohydrates
Carbohydrates are foods which give you energy. They are called carbohydrates because they are made of hydrocarbon molecules. Mostly they are either starches or sugars. Some foods which have a lot of carbohydrates in them are fruit, oatmeal, bread, honey, sugar, rice, corn, millet, barley, noodles, and alcohols like wine and beer.
For more about carbohydrates, check out this book from Amazon.com or from your library:
Carbohydrates for a Healthy Body, by Hazel King (2003).