13. Reverse transcriptase is an enzyme that can use RNA as a template to synthesize single strand DNA. As like all DNA polymerase, it needs a primer for the initiation of polymerization. If one wants to detect the expression levels of several protein-coding genes in mammalian cells with RT-PCR, which of the following primers is best for his reverse transcription reaction? (A) 5'-AAAAAAAAAAAAAAA-3' (B) 5'-TTTTTTTTTTTTTTT-3 (C) 5'-TATATATATATATATA-3 (D) 5'-ATGATGATGATGATG-3