One approach to studying the phosphoryation of the CTD of RNA polymerase II would be

A)the use of photo-crosslinking.
B)the use of [ $\alpha$ -32]ATP in the presence of a phosphorylase.
C)the use of [ $\gamma$ -32]ATP in the presence of a kinase.
D)the use of photo-crosslinking and the use of [ $\gamma$ -32]ATP in the presence of a kinase.
E)the use of photo-crosslinking and the use of [ $\alpha$ -32]ATP in the presence of a phosphorylase.