Correct Answer:
B. My aunt, who lives in Karachi, is a doctor.
The correctly punctuated sentence is My aunt, who lives in Karachi, is a doctor. This sentence uses commas correctly to set off a non-restrictive clause.
- The phrase "who lives in Karachi" provides additional, non-essential information about "My aunt." If removed, the sentence "My aunt is a doctor" still makes sense.
- Non-restrictive clauses must be enclosed by a pair of commas.
- Option A lacks both commas, incorrectly implying the clause is essential.
- Option C is missing the closing comma after "Karachi."
- Option D is missing the opening comma before "who."