A region's ____________________ is primarily determined by its average precipitation and average temperature over a long period of time.

What is characteristic of a thermal inversion? 

A)  Thermal inversions last only a few minutes to a few hours. 
B)  Thermal inversions exacerbate pollution problems. 
C)  Thermal inversion occurs when a layer of cold air prevents warm air from rising. 
D)  Normally, cool air near the Earth's surface expands and rises, carrying pollutants higher into the troposphere.

To which category do nitrates and phosphates belong? 

A)  organic plant nutrients 
B)  disease-causing agents 
C)  oxygen-demanding wastes 
D)  plant nutrients