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: Dental
Which of the following indicate extraction of upper first molars 
Select and explain. 
A. When they are rotated, B. When prognosis is poor, C. For mesial movement of second molars, D. When they are rotated
B: When prognosis is poor
Answer: B: When prognosis is poor 
Explanation: None