複選題23. Which of the following descriptions about exon, intron, 5' UTR, and 3' UTR is(are) correct (A) nonsynonymous mutation is a nucleotide change in exon that changes amino acid sequence of the encoded protein. (B) synonymous mutation is a single nucleotide change in intron that would never cause any change in the amino acid sequence of the encoded protein. (C) although not translated, the nucleotide sequence in the 5' UTR of mRNA corresponds to genomic sequence of exons but not introns. (D) although not translated, mutation in 3' UTR could profoundly affect mRNA stability. (E) mutation in intron may affect protein sequence by introducing mRNA splicing errors.