Final answer:
The primary source of energy that warms Earth's surface is light, specifically electromagnetic radiation from the Sun, which includes ultraviolet rays, visible light, and infrared radiation.
Step-by-step explanation:
The energy that warms Earth's surface comes primarily in the form of light, which is part of the electromagnetic spectrum. When we talk about the energy from the Sun that warms our planet, we're talking about a range of electromagnetic radiation that includes ultraviolet rays, visible light, and infrared radiation. While cosmic rays also reach Earth, they contribute a comparatively minute amount of energy. Similarly, the effects of magnetism and sound are not significant in terms of warming Earth's surface. Therefore, the correct answer to the question is A) Light.