The DNA sequence $\text{CCAAGAAGTCGACAAAA CA}$ is translated to produce the amino acid chain gly-ser-ser-ala-val-cys. Following a mutation, the length of the amino acid chain is reduced from six to two amino acids. The stop codon in mRNA is $\text{UGA}$. Identify which base in the DNA sequence was altered by the mutation?
- AA
- BC
- CG
- DT