Can you name the first three notes to “Have Yourself A Merry Little Christmas”? Do the poll first without listening to the song and then have a listen and let us know if your answer changed. I’ll post a spoiler with the answer later.
Well, I messed up the poll. Here are your choices:
CDE
CEF
CEG
EFG
EGA
EGC
GAC
GBC
GCD
GCE
Link to song
It’s the root, third and fifth of the chord (the fourth note is the octave root).
[spoiler]As burpo said, it’s a very common melody fragment. Just a regular old major triad, broken up into three separate notes. I’m guessing most people with at least a year of music lessons under their belt would notice this right away – then, it’s just a matter of seeing which of your combinations makes up a major triad. Luckily, you made it even easier by arbitrarily choosing to do it in C major – the first key (and scale) most people learn (if they start with piano, anyway).
If you had included MORE THAN ONE major triad in your list, then part of what you’d be testing is perfect pitch, which very few have (you’re basically born with it, or not).[/spoiler]
I didn’t mean to sound like a Scrooge – this kind of ear training is fun, helpful, and seasonally appropriate, so thanks!
My wife–the piano teacher–gives me guff all the time about my love of dissonance, in particular, the Major 7th chord. I love to put the M7th in where it’s not called for and, conversely, try to resolve a M7th chord (like the M7th in “Have Yourself…” at “…days of yore.”) The vibrations in my head are cosmic, man. 
Maj7 can be wistful and lovely, and classy, too. I think of “Stairway to Heaven” (“…and she’s buying…”), or Vince Guiraldi’s "Christmas Time Is Here." (skip to 14:16 for a juicy one).
That album is a blast! Makes me wanna get up and… .
Mr. Guiraldi uses a boatload of 9th chords all through the music, giving you a somber feel over a happy passage and vice versa (there are better ways to say this).
Got it right. 