Which of These Properly Illustrates the Principle of Isostasy

Multiple Choice

Which of these properly illustrates the principle of isostasy?

A) High-density crust floats on top of low-density mantle.
B) Mountains stand high because they are gravitationally balanced by their deep crustal roots.
C) When weight is added to the crust,the crust responds by rebounding upward.
D) When material is removed from the crust,the crust maintains the new,lower elevation.