The correct answer is: (a) RNA polymerase (along with its sigma subunit) can initiate transcription on its own.
More differences between prokaryotic and eukaryotic transcription:
• In prokaryotes transcription occurs in the cytoplasm (unlike in eukaryotes in nucleus) and it is simultaneous with translation,
• In prokaryotes there is only one type of RNA polymerase (in eukaryotes there are three types of them).
• There is no sigma subunit in eukaryotes, the initiation of transcription begins thanks to initiation factors.
• Promoter region in prokaryotes contains pribnow box, while in eukaryotes it contains TATA and CAT box.