Questions: Professor Tabarrok said in the video that there is a "problem" with the fact that flu shots create external benefits. What's the problem?

The answer is: The person getting the flu shot bears all of the cost.

Explanation for each option:

1. Benefits that fall on bystanders are hard to measure.
   While it is true that external benefits, or positive externalities, can be difficult to quantify, this is not the specific problem highlighted by Professor Tabarrok regarding flu shots. The issue is more about the distribution of costs and benefits rather than measurement.

2. Goods with social benefits are signs of communism.
   This statement is incorrect and reflects a misunderstanding of economic concepts. Goods with social benefits, such as public goods or those with positive externalities, are not inherently linked to communism. They are a part of economic discussions in various systems, including capitalism.

3. People are suspicious of goods that have broad social benefits.
   While some individuals might be skeptical of certain goods or policies, this is not the primary problem discussed by Professor Tabarrok in the context of flu shots. The focus is on the economic implications of who bears the cost versus who receives the benefits.

4. The person getting the flu shot bears all of the cost.
   This is the correct answer. The problem with flu shots creating external benefits is that the individual who receives the flu shot incurs the cost, while the benefits extend to others in the community by reducing the spread of the flu. This can lead to under-consumption of the vaccine, as individuals may not take into account the full social benefits of their vaccination.