This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Medicine
Drug used treatment of Acute promyelocytic leukemia- 
Select and explain. 
A. Arsenic trioxide, B. Tretinoin, C. Gefitinib, D. Dasatinib
A: Arsenic trioxide
Answer: A: Arsenic trioxide 
Explanation: Arsenic trioxide is effective and approved for treatment of relapsed or refractory acute promyelocytic leukemia (APL) cases resistant to all-trans retinoic acid (ATRA), but its effect on new cases of APL is not clear. Ref Davidson 23rd edition pg 789