Galileo Observed the Phenomenon of Solar Rotation in the Early

Galileo observed the phenomenon of solar rotation in the early 1600s by

A) watching bright regions of hydrogen gas drift across the sun.
B) noting the periodic (monthly) variation of auroral disturbances or northern lights.
C) watching sunspots move across the solar surface with a telescope.
D) measuring the Doppler wavelength shift of hydrogen spectral lines from east and west limbs of the Sun.