This is the normal nucleotide sequence on a dna strand: A-C-T-G-G-A-T what is a substitution?

(A.) A-C-T-G-C-G-A-T

(B.) A-C-T-G-A-T

(C.) A-G-T-G-G-A-T

(D.) A-C-U-G-G-A-U