Which sentence demonstrates proper noun usage?

The sentence that demonstrates proper noun usage is effective because it includes "Chicago," which is a specific name of a city. Proper nouns are unique identifiers, such as the names of people, places, or organizations, and they are always capitalized. In this case, "Chicago" specifically refers to a particular city, distinguishing it from any other city.

The other sentences contain common nouns, which refer to general items or concepts rather than unique entities. For example, in "I visited the city museum," "city museum" refers to a type of museum rather than a specific one. Similarly, "the car" in "The car is red" and "a dog" in "A dog is barking" are common nouns and do not specify a particular car or dog. Thus, they do not exemplify proper noun usage.