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
[{'content': 'Drug used treatment of Acute promyelocytic leukemia- \nSelect and explain. \nA. Arsenic trioxide, B. Tretinoin, C. Gefitinib, D. Dasatinib', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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', 'role': 'assistant'}]