Final answer:
The primer used in DNA replication is composed of RNA, which is synthesized by primase to provide a starting point for DNA polymerase.
Step-by-step explanation:
Strand initiation in DNA replication is accomplished when an enzyme lays down an RNA primer. Therefore, the primer is composed of RNA (d. RNA). During this process, the enzyme primase synthesizes a short strand of RNA nucleotides that are complementary to the DNA template strand. This RNA primer is essential as DNA polymerase can only add nucleotides to an existing strand of nucleic acid. The primer provides the necessary 3'-OH end for the nucleotide addition. After elongation, the RNA primer is removed and replaced with DNA nucleotides, and the DNA strand is completed by the action of DNA ligase.