[单选题]
If an element of atomic number 15 obb :te)tk)o7heqz7 3 haxnx )v4o1h3-vxrf gcp:0 g) pxs 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.