Why Was It Necessary for Bohr to Require That Electrons

Multiple Choice

Why was it necessary for Bohr to require that electrons remain in stationary orbits?

A) An electron must travel in a circular path.
B) It was required by the Heisenberg uncertainty principle.
C) No two electrons can be in the same region in the atom.
D) It was required by the Pauli exclusion principle.
E) Classical physics predicts that the electron should spiral into the nucleus.