Analysis: A, according to the physiological function of iron.
B, according to the physiological function of vitamins.
C, according to the physiological function of calcium.
D, according to the physiological function of iodine.
Answer: A. Iron is the main component of hemoglobin synthesis. Lack of it will lead to iron deficiency anemia, so it is wrong.
B, lack of vitamin A can cause night blindness, so it is wrong.
C, calcium is the main component of human bones and teeth, it makes bones and teeth have a hard structural support, when lacking, children and adolescents will suffer from rickets, and the elderly will suffer from osteoporosis, so it is correct.
D, iodine is the main component of thyroid hormone synthesis, lack of it will cause goiter, so it is wrong.
So choose C.
Comments: The new concept of "reasonable diet and scientific nutrition" has penetrated into the minds of modern people. In chemical investigation, the contents about six nutrients or chemical elements and human health have firmly occupied a place, including their physiological functions, main food sources, lack of symptoms, intake principles and so on.