Which of the following sentences contains a quote that has no grammatical, punctuation, or stylistic errors?

a.
ponyboy is reminded to stay innocent and stay pure when he is told, "stay gold."

b.
from the very beginning, readers are aware that something is not quite right in the novel 1984, as it begins "it was a bright cold day in april, and the clocks were striking thirteen."

c.
one critic complains "they’re sheep in wolves’ clothing who manage to write about bad things and make you feel good".

d.
herr bock, a former training professor at the ministry of state security, explains that, above all, an informer “need[s] to be honest, faithful, and trustworthy.”