According to "How to Think Like a Researcher," a chapter from How to Find Out Anything, one should begin research by asking answerable questions rather than open-ended questions. Based on the guidelines in the text, which is an appropriate research question?

An appropriate research question can be answered with specific information that can be researched and measured. The average income of dentists in the United States can be determined using income data and a defined time period. “Nice weather,” “better,” and “most difficult” are subjective terms, so choices A, B, and C are less clearly answerable.

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