Gene Methylation Can Be Detected Through the Use of Restriction

Gene methylation can be detected through the use of restriction endonucleases. Usually these are used in pairs where one enzyme will digest only unmethylated DNA in its recognition sequence while the other is insensitive to methylation. Which of the following statements is correct?

A) The enzyme that is insensitive to methylation serves as a control to make sure the inability of the other enzyme to digest DNA is not due to a mutation.
B) These are used in pairs since experiments have to be replicated and this one way of performing a replication of the experiment
C) The experimental design is flawed since there should be a third enzyme that would serve as a positive control
D) This experimental design is able to detect most of the methylated C residues in a particular region of DNA.