[单选题]
In radioactive dating, carbon-14 is often;ej+ 7fp4*+ htau klon used. This nucleus emits a single bmy/f-,bpq 9 dbeta particle when it decays.q pb/ m,fby-d9 When this happens, the resulting nucleus is
A. still carbon-14.
B. boron-14.
C. nitrogen-14.
D. carbon-15.
E. carbon-13.
