Choose the sentence with correct use of the non-restrictive clause:
A. The girl who won the contest is my sister.
B. The girl, who won the contest, is my sister.
C. The girl who won the contest, is my sister.
D. The girl who won the contest is my sister.
The correct form is "The girl, who won the contest, is my sister," using commas to set off the non-restrictive clause.