One Approach to Studying the Phosphoryation of the CTD of RNA

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.