What gas contributes to 78% of earth's modern atmosphere?
a. argon
b. nitrogen
c. oxygen
d. carbon dioxide

According to the diagram, what sources contribute to the phosphorus found in soil? according to the diagram, phosphorus found in soil contributes phosphorus to what other sources? (site 1)

According to the big bang theory, after the "bang," the universe remained dark until about  300,000 yearsone billion yearsthree minutesthree billion years  later, when neutral atoms began to form.

All but one describes an effect of aging on the digestive system. a) decreased acid secretion b) decreased elasticity of stomach c) capacity to resist damage decreases d) food remains in stomach for less time