Which change to one of the kits would make it useful for modeling proteins?

A. Set 1, add a box for phosphorous (P) atoms.
B. Set 2, add a box for sulfur (S) atoms
C. Set 3, replace the box of phosphorous (P) atoms with a box of sulfur (S) atoms
D. Set 4, replace the box of oxygen (O) atoms with a box of nitrogen atoms (N)