The right answer is B, the battery.
When an electron is accelerated through potential difference then the speed that it attain will be explained by energy conservation
here by energy conservation we can say that
change in kinetic energy of electron = electrostatic potential energy gained through given potential difference
kinetic energy is given as

electrostatic potential energy is given as

now by energy conservation

given that for electron



now by plug in values



So here it is accelerated through potential difference of 2559.4 Volts
The Electric field strength reduces or increases as the distance from the source increases or reduces respectively. It actually follows inverse square law.
The Electric Field strength reduces or increases by the square of the distance away from the source or toward the source respectively.