Stable Isotopes,with Low Atomic Numbers,have a N/Z Ratio of 1

Stable isotopes,with low atomic numbers,have a N/Z ratio of 1.What does that imply?

A) The number of neutrons equals the number of protons.
B) The number of neutrons equals the number of electrons plus protons.
C) The number of electrons equals the number of protons plus neutrons.
D) The atomic number equals twice the atomic mass.
E) The number of protons equals the number of electrons plus neutrons.