In which of the following ways are dna and mrna similar?
a) they are both always kept in the nucleus to keep them safe from damage.
b) they are both double stranded and must be unzipped during replication and transcription.
c) they both contain the entire genetic sequence of the original dna from their parent cell.
d) they both copy genetic code by forming a complementary sequence of nucleotides with an existing strand of dna.

Option (D).

Explanation:

DNA is present as a genetic material in all organisms except some viruses. DNA replication is the process of formation of copy of DNA molecule from the parental strand. Transcription is the process of formation of RNA molecules from the template DNA strand.

DNA and RNA copy the genetic code by the process of replication and transcription, respectively,  during which nucleotides complementary to the template DNA strands are added to the growing DNA or RNA chain.

Thus, the correct answer is option (D).