Final answer:
c. Vesto Slipher discovered the redshift of distant galaxies, providing evidence for the expansion of the universe.
Step-by-step explanation:
The redshift of distant galaxies was discovered by c. Vesto Slipher. In the early 20th century, Slipher used spectroscopy to study the spectra of spiral nebulae, which are now known to be galaxies.
He observed that the spectra of these galaxies showed a shift towards longer wavelengths, indicating that they were moving away from us. This discovery, known as the redshift, provided the first evidence for the expansion of the universe.