Question 2
Which four elements contribute most to building a living body?
The right answer is the one marked above.
Carbon, hydrogen, oxygen and nitrogen are the four that do most of the building. Every one of the four biological molecules is made largely from them.
Sulphur, phosphorus, sodium, potassium, calcium, magnesium, iron and chlorine matter too — a body cannot survive without them — but they are present in far smaller amounts.