I would like to thank whoever it was that wrote that piece of music: it has given me so much pleasure

• A. I would like to thank whoever it was that wrote that piece of music:
• B. I would like to thank whomever it was that has written that piece of music:
• C. I would like to thank whomever it might be that wrote that piece of music:
• D. Whoever it was that wrote that piece of music, I would like to thank because