For a Multielectron Atom,a 3s Orbital Lies Lower in Energy

Multiple Choice

For a multielectron atom,a 3s orbital lies lower in energy than a 3p orbital because

A) a 3p orbital has more nodal surfaces than a 3s orbital.
B) other electrons more effectively shield electrons in the 3s orbital from the nucleus.
C) other electrons more effectively shield electrons in the 3p orbital from the nucleus.
D) there are more p orbitals than s orbitals in a given shell.