To decode the Roman numeral XXIV, we use the additive principle. Roman numerals are primarily based on the additive system, where the values of the individual characters are added together.
In XXIV:
- X = 10
- X = 10
- I = 1
- V = 5
So, XXIV = 10 + 10 + 1 + 5 = 26.
Thus, the correct answer is: D. The additive.