The first stage of the cell cycle during which the cell matures and prepares to divide and copies its DNA; The stage the cell stays in the most?

What do isotopes of uranium have the same number of? what do they have a different number of? a) same number of protons; different number of electrons b) same number of protons; different number of neutrons c) same number of electrons; different number of protons d) same number of neutrons; different number of protons