Which sentence demonstrates correct punctuation with a nonessential clause?

• A. My sister, who lives in Seattle, is visiting.
• B. My sister who lives in Seattle is visiting.
• C. My sister, who lives in Seattle is visiting.
• D. My sister who lives in Seattle, is visiting.

Answer: (A)

Nonessential (nonrestrictive) clauses add extra information and are set off by commas on both sides. The best choice uses a pair of commas around the clause “who lives in Seattle,” signaling that this detail is additional and not needed to identify which sister is being talked about. So the properly punctuated sentence is the one with two commas: My sister, who lives in Seattle, is visiting. If the clause isn’t enclosed by commas (or is only partially enclosed), it changes the meaning or disrupts the flow, treating the clause as essential information or creating awkward punctuation.