Mrrzy: The song you were thinking of is this one, but I don't think it's the one SharonA asked for:

NOT IN A MILLION YEARS
(Gilbert O'Sullivan)

Every other morning
I lie in bed awake
And wonder why the dawning
Always has to break.
Could it be? it must,
As we all expect it to.
Could it be? I just
Simply haven't got a clue.
And what if it stayed behind,
Had itself a change of mind?

CHO: What would your impression be?
How would you react?
Would you simply smile and say,
"Don't be silly. go away.
Anyone can plainly see
It couldn't happen here,
Not in a million years."

So you think you're clever.
Well, if you really are,
Would you kindly tell me
How big is a star?
And what does it contain?
Is it metal or wood?
How much does it cost?
Is it really any good?
And what if they all came down,
Every one upon the ground? CHO.

Everyone knows one and one is two,
And all take for granted that it's true.
Everybody know that the world is round
Although it doesn't look it from the ground.
Everybody knows it's right.
But what if one and one were five,
And the world not really round;
Everywhere was just a huge flat piece of ground?

Look at all the animals
Living in zoos:
Elephants and tigers,
Lions and kangaroos.
Don't they all look cute
When they're hid behind a cage--
Funny when they laugh,
Exciting when they rage?
But what if they took control,
There and then reversed the role? CHO.