Why current remains same in series combination of resistors in all resistors and p. d. remains different?

Current at all points of a series circuit must be the same, because there's no place in the circuit where electrons are being manufactured, and no place where they're leaking out and falling on the floor. The nimber of electrons that leaves the loop is the same number that entered it. I'm not sure what is nmeant by "p.d. remains different" .