57. Which of the following statements about E. coli RNA polymerase is correct? (A) The enzyme is composed of four subunits, namely αβρσ. (B) It requires the assistance of a DNA helicase to unwind double-stranded DNA for initiation of transcription. (C) The o subunit is responsible for recognizing the promoter sequence. (D) The o subunit is dissociated from the enzyme complex when the mRNA synthesis is complete. (E) The growth direction of the RNA chain is from 3' to 5'.