Question: Who sings that was then this is now?

Disambiguated questions and answers:
context: No context provided
question: Who sings the song "That Was Then but This Is Now"?
short_answers: ABC

context: No context provided
question: Who sings the original version of the song "This Was Then, This Is Now"?
short_answers: The Mosquitos

context: The Monkees (at that point consisting of Micky Dolenz and Peter Tork) covered the song for Arista Records, who released their recording as a single and on the compilation album "Then & Now... The Best of The Monkees" in June 1986. The compilation album with three newly recorded songs was released by Arista and went platinum during the tour. “That Was Then, This Is Now” became the band's new single and a video for it was filmed at the Great Arena in Jackson, New Jersey on July 25. The video received heavy airplay on MTV, making the song a Billboard Top 20 hit the summer of 1986.
question: Who sings the cover version of the song "This Was Then, This Is Now"?
short_answers: The Monkees
wikipage: That Was Then, This Is Now (song)

context: No context provided
question: Who sings that was then this is now in 1983?
short_answers: ABC

context: "That Was Then, This Is Now" is a song written by Vance Brescia for his band the Mosquitos and recorded as the title track of their 1985 EP. Clive Davis of Arista records heard it and picked it to be the Monkees comeback single and theme of "The Monkees 20th Anniversary Tour", made in 1986.
question: Who wrote and sings that was then this is now?
short_answers: Mosquitos
wikipage: That Was Then, This Is Now (song)

context: "That Was Then, This Is Now" is a song written by Vance Brescia for his band the Mosquitos and recorded as the title track of their 1985 EP. Clive Davis of Arista records heard it and picked it to be the Monkees comeback single and theme of "The Monkees 20th Anniversary Tour", made in 1986.
question: Who sings that was then this is now as their comeback single?
short_answers: The Monkees
wikipage: That Was Then, This Is Now (song)

Long answers:
knowledge: content: "That Was Then but This Is Now" is a song by English band ABC. It was released in late 1983 as the lead single from their second studio album, Beauty Stab.
wikipage: That Was Then, This Is Now (song)

content: "That Was Then, This Is Now" is a song written by Vance Brescia for his band the Mosquitos and recorded as the title track of their 1985 EP.[3] Clive Davis of Arista Records heard it and picked it to be the Monkees' comeback single and theme of their 20th Anniversary Tour in 1986.[4]
wikipage: That Was Then, This Is Now (song)
long_answer: "That Was Then but This Is Now" is a song by English band ABC released in late 1983 as the lead single from their second studio album, Beauty Stab. "That Was Then, This Is Now" is a song written by Vance Brescia for his band the Mosquitos and recorded as the title track of their 1985 EP. Clive Davis of Arista Records heard it and picked it to be The Monkees' comeback single and theme of their 20th Anniversary Tour in 1986. 

long_answer: The Mosquitos sang the original That Was Then This Is Now. ABC sang the song in 1983, and The Monkees sang it as their comeback single.