Rice is the staple food of over half the world's population. It is the predominant dietary energy source for 17 countries in Asia and the Pacific, 9 countries in North and South America and 8 countries in Africa. Rice provides 20% of the worlds dietary energy supply, while wheat supplies 19% and maize (corn) 5%. Since, a large portion of maize crops are grown for purposes other than human consumption, rice is the most important grain with regard to human nutrition and caloric intake, providing more than one fifth of the calories consumed worldwide by humans. Rice contains high amount of carbohydrates compared to maize, wheat and barley. Thus, the correct answer is option D.