During times of high unemployment, colleges often observe an increase in enrollment even if tuition remains unchanged. Why（）
A. The benefit of attending college is lower because college graduates are less likely to find jobs
B. The opportunity cost of attending college is higher when unemployment is high
C. The opportunity cost of attending college is lower when unemployment is high
D. Students go to college even when the net benefit is negative
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Macroeconomics differs from microeconomics in that macroeconomics focuses on（）
A. prices in specific markets
B. production in specific markets
C. individual choices and group behavior in individual markets
D. the performance of national economies and ways to improve that performance
The marginal cost of an activity is the（）
A. change in the total cost of the activity that results from carrying out an additional unit of the activity
B. change in the level of the activity divided by the change in the cost of the activity
C. the total cost of the activity divided by the change in the level of the activity
D. the total cost of the activity divided by the level of the activity
The marginal benefit of an activity is the（）
A. total benefit of an activity divided by the level of the activity
B. same as the total benefit of an activity
C. total benefit associated with an extra unit of the activity
D. extra benefit associated with an extra unit of the activity
The number of U.S. households with access to the Internet is growing rapidly. Compared to 50 years ago, one would predict that when considering a major purchase, people today will gather（）
A. more information because the Internet has increased the cost of gathering information
B. less information because the Internet has increased the benefit of gathering information
C. more information because the Internet has lowered the cost of gathering information
D. less information because the Internet has lowered the cost of gathering information
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