How Do DNA Molecules Place Themselves in a CsCl Equilibrium

Multiple Choice

How do DNA molecules place themselves in a CsCl equilibrium gradient?

A) They continuously move toward the bottom of the gradient.
B) They stop momentarily at the point in the gradient equaling their buoyant density.
C) They continuously move toward the top of the gradient.
D) They stop permanently at the point in the gradient equaling their buoyant density.
E) All DNA molecules localize at the same point in the gradient.