A scientist studying the effects of radiation on DNA performs an experiment in which she exposes a sequence of nitrogen bases found in DNA to radiation. The DNA before and after the radiation is shown below. Use the evidence to determine whether a mutation has occurred, and if so, interpret that mutation in the answer sheet provided

Before Exposure: ATCGTCA; After Exposure: ATTCGTCA

A. No mutation has occurred to the DNA sequence.

B. A nitrogen base has been deleted from the DNA molecule.

C. A nitrogen base has replaced another nitrogen base in the DNA molecule.

D. A nitrogen base has been added to the DNA molecule.