Which sentence correctly uses commas to set off a nonrestrictive clause?

Which sentence correctly uses commas to set off a nonrestrictive clause?

• A. The scientist, who won the award, spoke tonight.
• B. The scientist who won the award spoke tonight.
• C. The scientist, who won the award spoke tonight.
• D. The scientist who won, the award spoke tonight.

Answer: (A)

Nonrestrictive clauses add extra information about a noun and are set off by commas. The phrase “who won the award” here is additional information about the scientist, and it can be removed without changing who the sentence is about. That makes it nonessential, so it should be surrounded by commas: The scientist, who won the award, spoke tonight.

If you omit the second comma, you’re treating the clause as essential to identifying the scientist, which changes the meaning: The scientist who won the award spoke tonight would imply there’s a specific scientist who won the award. The other two options either misplace punctuation or create an ungrammatical sentence, so they don’t fit the nonrestrictive structure.