This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: CNS Tumors, Subject name: Pathology
A metastatic carcinoma in the brain of an adult, most often comes from a primary in the: 
Select and explain. 
A. Stomach, B. Ovary, C. Oral cavity, D. Lung
D: Lung
Answer: D: Lung 
Explanation: Metastatic carcinoma in the brain of an adult, most often comes from a primary in the Lung. The five most common primary sites are lung, breast, skin (melanoma), kidney, and gastrointestinal tract, accounting for about 80% of all metastases.