Which of the Following Is True of "ON" and OFF

Which of the following is true of "ON" and OFF" retinal cells?

A) ON cells decrease their firing rate to a light placed onto the center of the field.
B) OFF cells increase their firing rate to a light placed onto the center of the field.
C) Rod bipolar cells are of the ON type.
D) Rod bipolar cells are of the OFF type.
E) ON cells help to detect a dark spot against a light background.