Professor: Different countries have different economic systems, but all economic systems have prosperity as their primary goal. Because people all want the same thing, there cannot be radical disagreement among people from different economic systems about practical economic matters. Thus all apparent disagreement in practical economic issues is illusory. Which one of the following most accurately describes a reasoning error in the professor's argument? ['The argument contradicts itself about whether there are in fact differences between economic systems in different countries.', 'The argument ignores the possibility that groups of people may share the same goal but not agree about how best to achieve that goal.', 'The argument bases a general conclusion about economic systems on one example of such a system, which there is reason to think is atypical.', 'The argument depends on using the key term "economic system" in two incompatible senses.']