The Energies for Removal of a 1s Electron from a H

The energies for removal of a 1s electron from a H atom, a He atom and a He⁺ ion are 2.18x10^-18 J, 3.94x10^-18 J, and 8.72x10^-18 J, respectively. These values indicate

A) ionization energies directly reflect the nuclear charge.
B) partially shielding results from electrons having the same principle and azimuthal quantum numbers.
C) s electrons effectively shield p electrons of the same principal quantum number.
D) shielding results only from electrons having lower principal quantum number.
E) ionization energy is independent of nuclear charge.