Which of the following sentences uses capitalization rules correctly?

The chosen sentence is correct because it adheres to capitalization rules by properly capitalizing "Red Sea," which is a proper noun referring to a specific geographical location. In English, names of specific places, such as oceans and seas, must be capitalized. Additionally, "sister" is not capitalized in this context since it is not used as part of a title or in place of a name; therefore, "My sister Abby" is the appropriate usage.

In contrast, the other options either incorrectly capitalize "sister" or "sea." These mistakes highlight the importance of recognizing the difference between common nouns, which are not capitalized, and proper nouns, which are. Thus, option C clearly demonstrates a correct application of capitalization rules.