Which Substance(s) Listed Below Would Be Expected to Have a Standard

Which substance(s) listed below would be expected to have a standard Molar Gibbs Free Energy of formation value equal to zero, D G ° _f = 0?
(Pay careful attention to the phase indicators.)

A) H₂ (g)
B) CO₂ (g)
C) NaCl (s)
D) H₂ O ( )
E) All of these.