Why are pollution cleanup efforts ineffective? 

A)  they often transfer pollutants from one part of the environment to another 
B)  we lack technology to clean up most pollution 
C)  too much effort and funding is focused on pollution prevention 
D)  because efforts are only effective with nonpoint sources, not point sources

Canada is the world's most tornado-prone country.

What can cause mutations in an organism's DNA? 

A)  x-rays 
B)  ozone 
C)  carbon dioxide (CO₂)  
D)  methane (CH₄)

The lithosphere is the top of the upper mantle and contains all the air surrounding the Earth.