Transcription in bacteria differs from transcription in a eukaryotic cell because __________________________. (a) RNA polymerase (along with its sigma subunit) can initiate transcription on its own. (b) RNA polymerase (along with its sigma subunit) requires the general transcription factors to assemble at the promoter before polymerase can begin transcription. (c) the sigma subunit must associate with the appropriate type of RNA polymerase to produce mRNAs. (d) RNA polymerase must be phosphorylated at its C-terminal tail for transcription to proceed.