Which of the following transcription regulators constitute the master set of transcription regulatory proteins whose expression is most required for generating induced pluripotent stem cells and for maintaining pluripotency? Choose three proteins. Your answer would be a three-letter string composed of letters A to F in alphabetical order, e.g. CEF.
(A) Myc
(B) Klf4
(C) MyoD
(D) Nanog
(E) Oct4
(F) Sox2