Question

a star that is several thousand times brighter than the sun with a temperature lower than 4,000 k would be classified as — a main - sequence star in spectral class b a white dwarf in spectral class b a main - sequence star in spectral class k or m a supergiant in spectral class k

Explanation:

On the Hertzsprung - Russell (H - R) diagram, stars are classified based on their luminosity (brightness) and temperature (spectral class). Main - sequence stars have a specific relationship between luminosity and temperature. White dwarfs are faint and hot. Supergiants are very luminous. Spectral class K or M stars have relatively low temperatures (lower than about 4,500 K). A star that is very bright (several thousand times brighter than the Sun) and has a low temperature (lower than 4000 K) would be a supergiant. In the spectral class system, cooler stars (lower temperature) are in spectral classes like K and M.

Answer:

a supergiant in spectral class K