Why is the sun important for us?

Hint: The Sun is located at the center of the Solar System at which the earth and the other planets revolve around the sun. The sun provides life–giving sources to earth. In the solar system, the sun is the powerful center of attention and holds the solar system together. The Solar system is located at the center of the Milky Way.

Complete Step by step solution
About the light and Heat energy from Sun:
Deep inside the core of the sun fusion process takes place. The process of fusion in the sun is known as the proton-proton chain. It begins with protons and by a series of steps turns them into helium. Because the total energy of the helium is less than the energy of protons that went into it, thus this fusion process releases energy.

Steps of fusion process,
1. The two pairs of protons fuse together and form two deuterons
2. Then each deuteron gets fuses with an additional proton which forms helium-3
3. Then the two helium-3 nuclei fuse to form beryllium-6, but it is unstable, due to which it disintegrates and form two protons and a helium-4
4. The reaction also releases two positrons, gamma rays and two neutrinos.
Thus, helium-4 atoms have less energy than that of $4$ protons and the heat and light streaming from the Sun came from this fusion reaction.

The solar energy is the radiant of light and heat from the sun. Thus, the solar energy is used in the evolving technologies like photovoltaic, solar heating, solar thermal energy etc. Solar energy is one of the attractive renewable energy sources because of its nonpolluting character and its inexhaustible supply, which is in contrast to the non-renewable sources of fossil fuels like coal, petroleum, and natural gas.

About the Gravitational force by sun:
Gravity is very important to us because the planets in our solar system move, the sun uses its gravity force to pull all the planets towards its center. The gravity force from the sun which makes our planet to move in a curved elliptical path in orbit. We could not live on Earth without it. The sun's gravity keeps Earth and other planets in orbit around it, which keeps the earth at a comfortable distance to receive perfect sunlight and warmth from the sun. It holds down our earth’s atmosphere and the air that the living beings need to breathe. Gravity is the phenomenon which holds our world together.

Thus, the Sun is more important for us because it gives light and heat energy from it and the gravitational force is also the most important one.

Hence the option (D) is correct.

Note: The sun’s atmosphere lies above its photosphere, the sun’s atmosphere consists of the chromosphere and the solar corona. The chromospheres will look like a reddish glow fringing the sun and the corona has huge white tendrils which extend millions of miles long. The chromosphere and corona will also emit visible light.