How did the development of quantum mechanics change Bohr's model of the atom?

a
Instead of being spread evenly throughout the atom, the electrons were in a cloud around the outside.

b
Instead of being a broad cloud of electrons, the electrons were organized into discrete levels, or shells.

c
Instead of being in open shells, the electrons were placed into orbitals based upon their probability distribution.

d
Instead of being on the outside of the atom, the electrons were found to be in a separate space.