Remember, that the phrase "x% of y" just means "y multiplied by x%."
Here the part that can be expressed many different ways is the x%, or in your case 25%.
25% = .25 = 25/100 = 1/4
This means the answers A, B, and C are all different ways to write 25 percent of N.
25% is NOT equal to 25, however. This is why the correct answer is D. 25 N = 25 * N and this is NOT equal to 25 percent of N.
I hope that helps.