[单选题]
If an element of atomic number nasggdpg ae-ovg762,8cdw /+ 15 has an isotopprb5k85su5khds m -s;e 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.