[单选题]
If an element of atomic number 15 has(5h y8ptt aq6:i k-;daijg,bb an isotope of mass number 3*x0qp6 c3mbln2,
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.