"How Can I Be Sure?" by The Young Rascals.

OK, more 60's: This moving Cavaliere/Brigati romantic ballad was written and recorded by their group in '67 - their 4th US hit, peaking at #4. Their highest-charting single with Eddie Brigati on lead vocals. Doubts of one-sided love. The beautiful accordion accompaniment gives it a French cabaret feel. French chanteuse Nicoletta's version sold 2 million copies worldwide. David Cassidy topped the charts with it in the UK and took it to #25 in the US in '72. Song? Group?
http://www.youtube.com/watch?v=TuKeSUUK-A4
http://www.youtube.com/watch?v=p1rpKz_52GE

Yesterday's answer: "Trumpet Voluntary" by Henry Purcell (not really!).

Yo, I should ask Henry for a refund! STILL a majestic piece even though he didn't write it.

http://www.youtube.com/watch?v=bRrss4kBi2M

http://www.youtube.com/watch?v=C-6zEzq-HM0