Telomerase is an enzyme which is a:

Telomerase is an enzyme that is a ribonucleoprotein. It is a complex of RNA and protein that is responsible for the addition of nucleotides to the ends of chromosomes, which helps to maintain the length of the chromosomes. So, the correct answer is option D. Notice that the other options are not correct. Repetitive DNA refers to sequences of DNA that are repeated multiple times in a genome, but it is not related to telomerase. RNA is a type of nucleic acid that is involved in the synthesis of proteins, but it is not the correct answer in this case. Simple protein refers to a protein that is not complexed with other molecules, but telomerase is a complex of RNA and protein.