Which of the following is an example of the phenomenon termed "RNA editing"? See Section 8.4 (Page 295) .
a. Co-transcriptional splicing of mRNA to remove introns
b. Posttranscriptional addition of a poly-A tail to the 3' end of mRNA
c. Posttranscriptional insertion of uracil nucleotides facilitated by a guide RNA
d. Co-transcriptional addition of a modified guanosine nucleoside to the 5'end of mRNA