Your answer is the first option or "C/kg." C/kg is a ratio for specific charge. C for the charge of the electron, kg for the mass of the electron. To find the specific charge we divide the two, which usually involves scientific notations and simplifying.
Maybe the picture helps. The blue block represents the cart with a mass of 3 kg. The person(black block) is pulling the cart to the right with a force F so that the acceleration a is 2 m/s². According to Newton's 2nd law: F = m*a.