Two straight wires separated by a very small distance run parallel to each other, one carrying a current of 4.0 A to the right and the other carrying a current of 7.8 A to the left.

answer: the correct answer for the fill in the blank is rods.

rods are the specialized photoreceptor cells that are present in the retina of human eye. they are responsible for vision in the night time ( also called scotopic vision). they have very low visual acuity and color distinguishing ability.

as they are responsible for vision in night time, therefore they are found predominantly in the nocturnal animals.