Предлоги оп, in, at спрятались от других слов словам найти своих друзей.
in
December
1991
Friday
4 o'clock
Christmas
noon
winter
11 o'clock
the morning
August​

In December
in 1991
on Friday
at 4 o'clock
on/at Christmas*
at noon
in winter
at 11 o'clock
in the morning
in August

* "At Christmas" we say when it's a longer time until Christmas. Like, "I'll see you at Christmas." (right now it is only October or something) Also, it could mean the days before and after Christmas

"On Christmas _Day_" we say to talk specifically about the 25th of December .