Aluminum has an atomic number of 13, so it has 13 protons. In its natural state, it does not have a charge, so it has an equal amount of electrons, 13. The atomic mass of aluminum is approximately 27. Since protons and neutrons make up that mass, and each of the particles are around 1 atomic mass unit, if there are 13 protons, then there are 27-13 neutrons, or 14 neutrons. So the first answer choice is correct.
