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: Medicine
Superior vena cava syndome is due to which type of lung carcinoma  a) Small cell  b) Squamous cell  c)  Adeno carcinoma   d) Undifferentiated 
Select and explain. 
A. ab, B. abc, C. acd, D. ad
A: ab
Answer: A: ab 
Explanation: None