Identify the sentence with correct use of the nonrestrictive clause:
A. My friend, who is a doctor, just opened her own clinic.
B. My friend who is a doctor just opened her own clinic.
C. My friend, who is a doctor just opened her own clinic.
D. My friend who is a doctor, just opened her own clinic.
The correct form is "My friend, who is a doctor, just opened her own clinic," using the nonrestrictive (or nonessential) clause set off by commas.