In Light of Modern Solar System Theory, Why Do the Orbits

Multiple Choice

In light of modern solar system theory, why do the orbits of the planets all lie in the sameplane?

A) The Sun's gravity forced them into these orbits.
B) The angular momentum of the solar system was kept to a minimum this way.
C) The early solar nebula flattened into a disk.
D) Comets would have wiped out any not in this protected plane.
E) This happened purely by chance.