A star much cooler than the sun would appear (a) red; (b) blue; (c) smaller; (d) larger.

option A and C

Explanation:

Star is cooler than the sun it means the energy emitted by the star will also be less than the sun.

Wavelength is inversely proportional to the energy. Star energy is less so wavelength will be maximum.

Hence, the star will appear Red because the wavelength of red light is maximum.

When the size of the star is large the energy produced by the star will be more and if the star is cooler that means the star is smaller.

Hence, the correct answer is option A and C