Concept:In the hexadecimal number system, decimal values from 10 to 15 are written using the letters A to F.Explanation:The hexadecimal system has base 16, so its digits are 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F.After the digit 9, letters are used to represent the next values.Therefore, A=10, B=11, C=12, and D=13.Continuing this pattern, E=14 and F=15.Hence, the hexadecimal digit D corresponds to the decimal number 13.Answer:C. 13