[单选题]
In radioactive dating, carbon-14 is often used. Th tvmtis7a1 v/3q 8jkcl3o2b 6qis nu;.uy+ 9horlb:mv noq)cleus emits a single beta particle when it decays. When this happens, t+9bl um v. :oyor;hq)nhe resulting nucleus is
A. still carbon-14.
B. boron-14.
C. nitrogen-14.
D. carbon-15.
E. carbon-13.