21. Which of the following statements about RNA polymerase is NOT correct? (A) DNA moves through a channel in RNA polymerase and makes a sharp turn at the active site (B) Sigma factor is required for both the initiation and elongation steps of RNA synthesis (C) Sigma factor changes the DNA-binding properties of RNA polymerase so that its affinity for general DNA is reduced and its affinity for promoter is increased (D) Core RNA polymerase of bacteria can synthesize RNA from a DNA template but cannot initiate transcription at the correct site