I visited the Eiffel Tower and the Louvre Museum while exploring Paris with my friend Sarah and her brother, John.
In this sentence:
1. "Eiffel Tower" and "Louvre Museum" are two proper nouns. These are specific names of famous landmarks in Paris, France.
2. "friend" and "brother" are common nouns. They are general terms used to refer to individuals without specifying their names or identities.
The sentence describes a visit to two well-known places in Paris, Eiffel Tower and Louvre Museum, and mentions two individuals, Sarah and John, who accompanied the speaker on this trip.