Which sentence uses a nonrestrictive clause with commas correctly?

Which sentence uses a nonrestrictive clause with commas correctly?

• A. The lab, which was new, failed.
• B. The lab which was new, failed.
• C. The lab, which was new failed.
• D. The lab which was new failed.

Answer: (A)

Nonrestrictive clauses add extra information about a noun and are set off by commas. Here, the clause “which was new” gives additional detail about the lab but is not needed to identify which lab is being talked about. That extra information should be enclosed with commas, so the natural, correct form is: The lab, which was new, failed. The commas show that the main idea is that the lab failed, and the note about it being new is optional.

The other options misplace or omit punctuation or misuse which for a restrictive clause. One option places the comma at the wrong spot and reads as if the clause is restrictive, which changes how the sentence flows. Another option leaves out the closing comma around the nonrestrictive clause, making the boundary of the extra information unclear. The final option drops the necessary commas entirely and uses which in a way that would imply a restrictive clause; in standard American usage, that would be written with a that if it were truly restrictive, but that changes the meaning here.