About 25 of the 92 natural elements are known to be essential to life. Which 4 of these 25 elements make up approximately 96 percent of living matter?
a) Carbon, Hydrogen, Nitrogen, Oxygen
b) Sodium, Potassium, Calcium, Magnesium
c) Iron, Zinc, Copper, Iodine
d) Phosphorus, Sulfur, Chlorine, Fluorine
