Which best corrects the run-on sentence? auroras illuminate the northern horizon they have a greenish glow or sometimes a faint red one.
a. auroras illuminate. the northern horizon in a greenish glow and sometimes a faint red one.
b. auroras illuminate the northern horizon. with a greenish glow or sometimes a faint red one.
c. auroras illuminate the northern horizon. they have a greenish glow or sometimes a faint red one.
d. auroras illuminate the northern horizon, a greenish glow or sometimes a faint red one.