Explanation:
The moon appears big when it is close to the horizon, and this is because of an optical illusion. This phenomenon is known as the moon illusion. The moon illusion has been studied by scientists for centuries, and there is still no clear consensus on why it occurs. However, there are some theories that attempt to explain this illusion.

Theory of Distance Perception:
One theory is that the moon appears larger when it is near the horizon because of our perception of distance. When the moon is closer to the horizon, it is viewed against a background of familiar objects such as trees, buildings, and mountains. This makes our brain perceive the moon as being farther away than it actually is. Since the brain knows that the moon is very large, it compensates for the perceived increase in distance by making the moon appear larger.

Theory of Angular Size:
Another theory is that the moon appears larger when it is near the horizon because of its apparent size. The moon is actually the same size when it is near the horizon as when it is high in the sky. However, when the moon is near the horizon, it is viewed through a greater thickness of the Earth's atmosphere. This causes the light from the moon to be refracted, or bent, which makes the moon appear slightly larger.

Conclusion:
Therefore, the correct answer is option 'C' - the moon appears big because it is near to the earth. When the moon is close to the horizon, it is viewed against a background of familiar objects, and our brain perceives it as being farther away than it actually is. Additionally, the moon appears larger because of the way that its light is refracted as it passes through the Earth's atmosphere.

"When the moon is near the horizon, the ground and horizon make the moon appear relatively close. Because the moon is changing its apparent position in depth while the light stimulus remains constant, the brain's size-distance mechanism changes its perceived size and makes the moon appear very large.
I hope you got your answer.