What best describes biologists' current hypothesis about the production of the Earth's atmospheric oxygen? 

A)  Photosynthesis by terrestrial plants produces atmospheric oxygen. 
B)  The breakdown of iron ore deposits produces atmospheric oxygen. 
C)  Photosynthesis by photosynthesizing bacteria produces atmospheric oxygen. 
D)  Chemosynthesis by aquatic plants produces atmospheric oxygen.

Which statement best characterizes the effect of human events on the environment? 

A)  Feedback is usually immediate. 
B)  It is predicted that the environment is diverse. 
C)  Long delays exist between events and responses. 
D)  Our generalizations are based upon many experiences.

Which type of radiation is the most highly penetrating? 

A)  alpha 
B)  gamma 
C)  beta 
D)  ultraviolet

What usually happens to the energy during an energy transformation? 

A)  It ends up as chemical energy that performs useful work. 
B)  It ends up as low-quality heat energy that flows into the environment. 
C)  It ends up as electrical energy that performs useful work. 
D)  It ends up as mechanical energy that performs useful work.