B, calcium is the main element of bones and teeth, lack of children and adolescents will suffer from rickets, the elderly will suffer from osteoporosis, so B is wrong;
C, zinc affects people's development, loss of appetite, growth retardation, dysplasia, easy to suffer from dwarfism, so C is correct;
D. Long-term selenium deficiency will affect the integrity of cell membrane, leading to decreased vision and various eye diseases, so D is wrong.
So choose C.