This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Which of the following drug has been approved for the treatment of cervical dystonia: 
Select and explain. 
A. Botulinum toxin A., B. Onabotulinum toxin A., C. Botulinum toxin B., D. All of the above.
C: Botulinum toxin B.
Answer: C: Botulinum toxin B. 
Explanation: None