The following diagram which shows two forces, X and Y, applied onto an
object.
Х
What should be the magnitude and direction
of a third force which will cause the object to
remain stationary?
(A)
(B)
(C)
X-Y to the left
X + Y to the left
X-Y to the right
X + Y to the right

its lower due to the doppler effect.: apex

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.