Hint: Stars have different colours which are due to the multitude of the temperatures their surface possesses. It is the temperature which defines the colour of the stars.Using the above parameter we will explain the colour indication as temperature.
Complete step by step solution: Colours of the stars are an indicator of their temperatures, their temperature is not because of colour but their colour is because of temperature. We have different types of stars such as supergiant and giant stars, medium sized stars and dwarf stars. Larger the star more will be the gravitation and more fast will the fusion reaction (two hydrogen atoms fuse into a heavy nucleus).
Large stars will have more fuel combustion than dwarf stars so their temperatures are also high as compared to dwarf stars. Larger stars are why they are hotter than dwarf stars. Stars having blue colour are hot and the stars having red colour are cold stars which are generally dwarf stars. Scientists have categorised the stars into class O, M and B , where class O and B stars are the hottest(blue in colour) and class M stars are the coolest ones(red in colour). From the above conclusion we have option D as the correct option.
Note:As the colour of the stars is due to the variation of temperatures, similarly the shape of the stars is due to the balance of two forces. One is gravity that wants to compress the star into its core. Another one is the expansion which opposes the compression. Expansion takes place due to the nuclear fusion reaction in the core.