Which identity could be used to rewrite the expression x^4-100? a) quadratic formula b) two squares c) sum of cubes d) difference of squares

100 is the square of 10, or 10^2.
x^4 is the same as the square of x^2, or (x^2)^2.
You can rewrite the expression clearly showing the squares:
(x^2)^2 - 10^2
Since both x^4 and 10 are squares, and the operation between them is a subtraction, this a difference of two squares.
Choice D.