A formal region is defined by official boundaries or uniform characteristics, such as language, climate, or economic activity.
Among the options given:
- French-speaking Canada is a formal region because it has a defined area where French is predominantly spoken.
- America's Corn Belt is also considered a formal region due to its distinctive agricultural practices and characteristics related to corn production.
- San Francisco's Chinatown is more of a cultural or ethnic neighborhood rather than a formal region.
Given these explanations, the correct answer to which is an example of a formal region would be both French-speaking Canada and America’s Corn Belt. Based on your choices, if the prompt asks for just one example, I would suggest selecting French-speaking Canada or America's Corn Belt, but the option “All are examples of formal regions” is incorrect as San Francisco's Chinatown does not fit the formal region definition.
So, the most accurate answer among the choices provided would be: French-speaking Canada or America's Corn Belt, depending on the context you are aiming for.