The perennial question, mart. In a 20th Century Fox musical, circa 1941, - black & white, of course - "Sun Valley Serenade", the Glenn Miller orchestra played the catchy "I Know Why and So Do You".
'Why do robins sing in December,
Long before the springtime is due.....
So why do I see rainbows
when I'm in your arms?
I know why and so do you."
A film which also featured 'Chattanooga Choo- Choo', (Harry Warren & Mack Gordon); The Nicholas Brothers & Dorothy Dandridge to override a daft plot, didn't need any reservations.