Which of the following atoms are isotopes of each other? (1) An atom with 17 protons and 18 neutrons

(II) An atom with atomic number 16 and atomic mass 32

(III) An atom with atomic number 15 and atomic mass 32

(IV) An atom with 17 protons and 20 neutrons

A. I and II

B. II and III

C. III and IV

D. I and IV