This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorders of pituitary gland, Subject name: Medicine
Which is the most common functioning tumour of pituitary? 
Select and explain. 
A. GH secreting tumor, B. Prolactinoma, C. ACTH producing adenoma, D. Oncocytoma
B: Prolactinoma
Answer: B: Prolactinoma 
Explanation: MC Functioning tumour of pituitary: Prolactinoma MC tumor of pituitary: Non- functioning adenoma