Enable humans to see and detect the color of different objects.

The given blank can be filled with photoreceptors.

Explanation:

The cells in the retina, which reacts towards light are known as photoreceptors. Their differentiating characteristic is the existence of the huge concentrations of the tightly packed membrane, which comprises the photopigment rhodopsin. The photoreceptors in the eyes allow humans to observe and determine the color of various objects.

because u need two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei to form isotopes.

so since they all have the same shape? i mean maybe because m& m and reeses are both chocolates