[单选题]
If an element of atomic1 y9tfzpfdy*f2* t n9y number 15 has an isa)fm*ve:r9/ vnl z5e sotope of mass 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.