Question: Who sings that was then this is now?
Disambiguated questions and answers: question: Who sings the song "That Was Then but This Is Now"?
Who sings the original version of the song "This Was Then, This Is Now"?
Who sings the cover version of the song "This Was Then, This Is Now"?
answer: ABC
The Mosquitos
The Monkees
question: Who sings that was then this is now in 1983?
Who wrote and sings that was then this is now?
Who sings that was then this is now as their comeback single?
answer: ABC
Mosquitos
The Monkees
Natural Questions answer: The Monkees (from the Wikipedia article "That Was Then, This Is Now (song)")