Just as optical astronomers observe the visible light emitted by objects such as stars and galaxies, radio astronomers can also observe the radio waves emitted by these objects, as well as the radio waves emitted by gas and dust. However, radio telescopes are different from optical telescopes in important ways. In general, compared to optical telescopes, radio telescopes are

the electric field is a “force field” around a charged object that illustrates the direction the electric force would push an imaginary 

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.