How does the concentration of ribonucleotide triphosphates play a role in the regulation of initiation?

A)a high concentration of ATP is required to form the open-promoter complex
B)high concentration of both ATP and GTP are required to form the open-promoter complex
C)the single nucleotide binding site of RNA polymerase undergoes a conformational change after the first nucleotide to allow subsequent nucleotides to bind more readily
D)binding of the first nucleotide requires a half-saturating concentration of ~100 $\mu$ M while the half-saturating concentration for subsequent nucleotides is only ~10 $\mu$ M
E)none of the above