Final answer:
Quasars being located in distant galaxies and having redshifted spectra provide evidence that they were more common in the early stages of the universe. So, the correct option is D.
Step-by-step explanation:
The correct answer is d) Both a and c are correct. This is because both statements a) and c) provide evidence that quasars were more common in the early stages of the universe. Statement a) mentions that quasars are located in distant galaxies. Observations with the Hubble Space Telescope have shown that quasars are indeed located at the centers of galaxies, indicating that they were more common in the early stages of the universe. Statement c) mentions that quasars have redshifted spectra. Redshift is the phenomenon where light from an object is shifted towards longer wavelengths, indicating that the object is moving away. The redshifted spectra of quasars suggest that they are located at great distances, which further supports the idea that they were more common in the early stages of the universe.