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
True about measles is/are  a) Incubation period (I.P.) is 10-12 days  b) Confunctivitis common  c) Rash starts on abdomen  d) Koplik spots are seen on fundus examination 
Select and explain. 
A. ab, B. bc, C. cd, D. bd
A: ab
Answer: A: ab 
Explanation: None