Read the following paragraph about the Sun.
Our Sun is at the center of our solar system. It is not even near the center of the Milky Way galaxy. The Sun is an ordinary yellow star. It is medium-sized but compared to Earth, it is huge. But other stars are far larger. The Sun warms the Earth and provides the energy for life. But other stars are much hotter. The Sun's temperature at the surface is about 6,000°C which is far cooler than a blue star. The surface of a blue star, the hottest colour, reaches 28,000°C.
At the surface, how much hotter than the Sun is the blue star?
(B) About 28,000°C
(D) About 22,000°C.