[单选题]
If an element of atomic number 15 u*wk7 w9ugf-a has an isotope of mass wk +-6fnv.: wt8kwqvv number 32,
A. the number of neutrons in the nucleus is 15.
B. the number of neutrons in the nucleus is 17.
C. the number of protons in the nucleus is 17.
D. the number of nucleons in the nucleus is 15.