Detective dupin

at paris, just after dark one gusty evening, i
sat before a warm fire with my friend, the famous
detective c. auguste dupin, in his little back
library. for one hour at least we had maintained
a profound silence; while each, to any casual
observer, might have seemed intently occupied
with the flickering of the flames in the hearth. for
myself, however, i was mulling over the mystery
of marie rogêt that we had worked on some
years before. i looked upon it, therefore, as
something of a coincidence, when the door of
our apartment was thrown open and in walked
our old acquaintance, monsieur g - - , the
prefect of the parisian police.
we gave him a hearty welcome. he was an
amusing fellow, if a bit of an oaf, and we had not
seen him for several years. we had been sitting
in the dark, and while g - - immediately began
talking, dupin rose to light a lamp. g - - said
he urgently wanted to discuss with dupin some
official business that was causing him a great
deal of trouble. when he heard that, dupin sat
down without lighting the wick.
"if it is any point needing careful thought,"
observed dupin, as he blew out the match, "we
shall examine it to better purpose in the dark."
"that is another of your odd notions," said
the prefect, who had a habit of calling everything
"odd" that he didn't understand, which meant
that he lived amid a world of "oddities."
"very true," said dupin, as he rolled towards
his visitor a chair.
"and what is the difficulty now? " i asked.
"the fact is, the business is very simple
indeed, and i have no doubt that we can manage
it by ourselves; but then i thought dupin would
like to hear the details of it, because it is so very
odd."
"simple and odd," said dupin.
"why, yes; and not exactly that either. the
fact is we have all been a good deal puzzled
because although the case is so simple, it confuses
us altogether."
"perhaps you are being fooled because the
answer seems too simple," said my friend.

adapted from edgar allan poe's "the purloined letter," 1917

why is the prefect's visit a coincidence?
a.
the narrator had been thinking about an odd case, and the prefect has lived amid a world of oddities for some years.
b.
the narrator was just thinking about the m. rogêt case in which he and dupin worked with the prefect some years before.
c.
the narrator and dupin are sitting in the dark, as they had been when they last saw the prefect some years before.

pls