[单选题]
If an element of atomqc 0s8x*cu w2g2ncmg0vg(a/u ag9)d3rbxw2 j7held ( ic number 15 has an isotope 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.