The answer is d. Binds to DNA, makes mRNA from DNA, detaches.
RNA polymerase is an enzyme involved in transcription, a process of copying DNA into messenger RNA (mRNA). In the transcription, RNA polymerase first binds to DNA separating its two strands. Then, it adds ribonucleotides to the complementary nucleotides on DNA strand and, thus, it makes mRNA from DNA. After mRNA is synthesized, RNA polymerase detaches from DNA, freeing the new mRNA.