12.What will you find if you compared the DNA sequence of a gene with the sequence of the mature mRNA that was transcribed from the gene? (A) The mRNA is shorter because each codon of three bases encodes only one amino acid；(B) The mRNA is shorter because it does not contain introns；(C) The mRNA is longer because each codon of one amino acid encodes three bases；(D) Both are the same length.