A figure intended to represent an abstract quality is personification.
As in given line abstract quality of sun is there "faithful" so the correct option is C.
All other options like "irony" are something different figure of speech which means in opposite to that.
Option C "paradox" means something combines contradicts features or qualities.
Options D and E are wrong options as "oxymoron" again some contradictory terms
and the poetic license is altogether a different term
So, in short, Option C is the correct option.