What is the completely factored form of d4 - 8d2 + 16?

What is the completely factored form of d4 - 8d2 + 16?

A) (d2 + 4)(d2 - 4)
B) (d2 - 4)(d2 - 4)
C) (d2 + 4)(d + 2)(d - 2)
D) (d + 2)(d - 2)(d + 2)(d - 2)