Global warming
a. has not yet been observed.
b. has been caused by increasing levels of carbon dioxide in the atmosphere.
c. has led to a depletion of the ozone layer in the atmosphere.
d. has no serious consequences.
b
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Radioactivity Basics: Scandium 
Sc decays by emitting a positron. What isotope is the product of this decay?
A. 
Sc
B. 
Sc
C. 
Ca
D. 
Ca
E. 
Ti
According to the way the layers of Earth's atmosphere are defined in the following figures, the atmosphere of Venus has only _________ distinct layer(s).
a. one b. two c. three d. four e. five
Doubling the f-number of a camera lens will change the light intensity admitted to the film by what factor?
a. 1/4 c. 1/2 b. 4 d. 2
In a problem using energy considerations to solve for the speed of a ball thrown from the top of a building when it strikes the ground below, where should the potential energy have its zero value?
a. It should be at the level from where the ball is thrown. b. It should be at the ground level where the ball hits. c. It should be slightly below ground level so the potential energy is always positive. d. It doesn't matter since only differences in potential energy matter in solutions.